Image sensor and method of manufacturing the same

[0001] 1. Field of the Invention

[0002] The present invention relates to a device for converting photons into charge packets, and more particularly to an image sensor with a metal wiring and a method of manufacturing the image sensor.

[0003] 2. Description of the Prior Art

[0004] An image sensor is a device for converting one or two-dimensional optical image into an electrical signal. The image sensor is a kind of a solid-state image sensor which is generally divided into a CMOS (Complementary Metal Oxide Semiconductor) image sensor and a CCD (Charge Coupled Device) image sensor.

[0005] The CMOS image sensor converts an optical image into an electrical signal, and employs a switch mode to detect outputs one by one using MOS transistors which are made as many as the number of pixels by use of CMOS manufacturing technique. In particular, the CMOS image sensor has advantages in that a driving mode is simple, various scanning modes can be embodied, and a signal processing circuit can be integrated into a single chip, which can miniaturize a chip. In addition, the CMOS image sensor is inexpensive and consumes a low power, because of utilizing a compatible CMOS technique.

[0006] The CMOS image sensor generally includes a pixel array and a peripheral circuit. In particular, the pixel array mainly consists of a photodiode for receiving incident light and a peripheral cell for converting the received light into an electrical signal. The photodiode has to secure a region occupied by the photodiode to receive much light.

[0007] In the case of securing the occupied region, there is a problem in that the pixel array is largely sized. In addition, since the region occupied by the pixel array is determined after a peripheral cell region is secured, there is a limitation of reducing a size of the pixel array. Accordingly, a fill factor (i.e., a ratio of the photodiode to the pixel array) is up to 30% at present.

[0008] Such as, a conventional CMOS image sensor has some advantages, but it is difficult to enlarge an area to be occupied by the photodiode, which may not obtain an image of high resolution.

[0009] Accordingly, the present invention has been made to solve the above-mentioned problems contained in the prior art, and an object of the present invention is to provide an image sensor capable of enlarging an area to be occupied by a photodiode.

[0010] Another of the present invention is to provide a method of manufacturing an image sensor of which an area occupied by a photodiode can be easily enlarged.

[0011] In order to accomplish this object, there is provided an image sensor comprising: a substrate with devices formed thereon, the devices including a photodiode and gate electrodes; a metal wiring of a transparent conductive material formed on the substrate for transferring signals of the devices to a circuit; a passivation film formed on the metal wiring for protecting the devices; a color filter formed on the passivation film for embodying an image; and a microlens formed on the color filter for collecting light.

[0012] According to another aspect of the present invention, there is provided a method of manufacturing an image sensor comprising the steps of: forming devices including a photodiode and gate electrodes on a substrate; forming a lower metal wiring of a transparent conductive film pattern on the substrate to transfer signals of the devices to a cirsuit; forming a plug formed on the lower metal wiring, the plug being connected to the lower metal wiring; forming an upper metal wiring of a transparent conductive film pattern on the plug, the upper metal wiring being connected to the plug; forming a passivation film on the upper metal wiring; and forming a color filter and a microlens on the passivation film.

[0013] With the present invention, all or a portion of the metal wiring consisting of the lower metal wiring, the plug, and the upper metal wiring is formed in a transparent conductive film pattern. As such, the metal wiring can be formed on the photodiode, so that the area occupied by the photodiode can be easily enlarged. That is, the metal wiring of the transparent conductive film pattern is employed, which does not impede transfer of light to the photodiode.

[0014] The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0015] FIG. 1 is a schematic view depicting a layout of a pixel array of an image sensor according to a preferred embodiment of the present invention;

[0016] FIG. 2 is a cross-sectional view of an image sensor according to a preferred embodiment of the present invention; and

[0017] FIGS. 3A through 3F are cross-sectional views depicting a process of manufacturing an image sensor according to a preferred embodiment of the present invention.

[0018] Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, and so repetition of the description on the same or similar components will be omitted.

[0019] FIG. 1 is a schematic view depicting a layout of a pixel array of an image sensor according to a preferred embodiment of the present invention.

[0020] Referring to FIG. 1, a pixel diode includes a photodiode 10 for detecting light and four transistors, which form a unit pixel. Among four transistors, a transfer transistor 12 is to transfer a charge stored in the photodiode to a floating diffusion region, a reset transistor 14 is to reset the floating diffusion region as a supply voltage level, a drive transistor 16 serves as a source follower, and a selection transistor 18 is to receive a pixel data enable signal and output a pixel data signal.

[0021] The pixel array is designed with a metal wiring 20 for transferring a signal to the device. The metal wiring 20 may be designed on the photodiode 10. The reason is because the metal wiring 20 is made of a pattern of a transparent conductive film consisting of a transparent conductive material. More specifically, since the metal wiring 20 does not impede when the photodiode 10 receives the light, the metal wiring 20 may be formed on the photodiode 10.

[0022] Accordingly, it is possible to easily enlarge an area occupied by the photodiode 10 in the pixel array. In practice, a ratio of the photodiode to the pixel array can be increased by above 50%.

[0023] A process of manufacturing the image sensor made of the transparent conductive film according to the present invention will now be described.

[0024] Devices containing photodiodes and gate electrodes are formed on a substrate. More specifically, a device isolation film is formed on the substrate. At that time, a trench isolation film is selected as the device isolation film. Then, the photodiodes and the gate electrodes are formed on the substrate. At that time, the gate electrode is formed as a transistor. An interlayer insulation layer is formed on the substrate, and then the substrate is subjected to a contact forming process to achieve an electric connection.

[0025] After the devices on the substrate, a process of forming a metal wiring is implemented with respect to the substrate. More specifically, a transparent conductive film of a transparent conductive material is formed on the substrate. The transparent conductive material is selected from InO, SnO, ZnO, MgO, or the like. Any one of the above materials is preferably selected, but a mixture of at least two elements may be utilized. In the case of the transparent conductive film of the transparent conductive material, a single film is preferably formed on the substrate, but at least two films may be formed thereon. For example, the transparent conductive film may be composed of a first InO film and a second SnO film. The transparent conductive film is patterned to form a transparent conductive film pattern and thereby form a metal wiring. More specifically, after forming the transparent conductive film, the substrate is subjected to an oxygen plasma process or a thermal annealing process under an oxygen atmosphere, so as to form the metal wiring. Te oxygen plasma process is preferably implemented under conditions of a pressure of 5 to 10⁻⁵ Torr and a power of 100 to 1,000 W. The thermal annealing process is preferably implemented at a temperature of about 350 to 600° C.

[0026] The metal wiring consists of a lower metal wiring, an upper metal wiring, and a plug for connecting the lower and upper metal wirings. Accordingly, after forming the lower metal wiring of the transparent conductive film pattern the above process, the plug connected to the lower metal wiring is formed, and then the upper metal wiring connected to the upper metal wiring is formed, thereby completing the metal wiring. At that time, the upper metal wiring may be formed by the same process as that of the lower metal wiring. Preferably, the plug is a tungsten plug, and may be made of a transparent conductive material. Preferably, an interlayer insulation film pattern is interposed between the lower metal wiring and the upper metal wiring so as to form the plug.

[0027] After forming the metal wiring, a passivation film is formed on the metal wiring so as to protect the underlaid devices from being subjected to the external environments. Then, a color filter is formed on the passivation film to embody an image. At that time, the color filter mainly consists of red R, green G, and blue B. A microlens is formed on the color filter to collect incident light.

[0028] As such, the image sensor according to the present invention includes, as shown in FIG. 2, a substrate 100 with devices consisting of photodiodes and gate electrodes formed thereon, a metal wiring 120 of a transparent material formed on the substrate 100, a passivation film 160 formed on the metal wiring 120, a color filter 180 formed on the passivation film 160, and a microlens 200 formed on the color filter 180. The metal wiring 120 consists of a lower metal wiring 120a, a plug 120b, and an upper metal wiring 120c. In particular, because of the plug 120b, an interlayer insulation film pattern 140 is interposed between the lower metal wiring 120a and the upper metal wiring 120c.

[0029] As such, the image sensor of the present invention includes the metal wiring 120 made of the transparent conductive material. The reason why the metal wiring 120 is formed on the photodiode is because the metal wiring 120 does not block the light incident onto the photodiode. Accordingly, the area occupied by the photodiode can be enlarged. Increased ratio of the photodiode to the pixel array may allow an image of a high resolution to obtain.

[0030] A process of manufacturing the image sensor according to one preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0031] FIGS. 3A through 3F are cross-sectional views depicting a process of manufacturing an image sensor according to a preferred embodiment of the present invention.

[0032] Referring to FIG. 3A, devices are formed on a substrate through a front-end-of-line (FEOL) process. First of all, a transistor consisting of a gate electrode 32 and a source/drain electrodes 36a and 36b is formed on the substrate. An interlayer insulation film pattern 40 having a contact hall is formed on the substrate 30 with the transistor formed thereon, and a tungsten plug 34 is formed in the contact hall. As a result, the substrate 30 including the devices having the photodiode and the gate electrode 32 of the transistor has been provided.

[0033] Referring to FIGS. 3B and 3C, a lower metal wiring 50a is formed on the substrate 30 with the devices formed thereon. More specifically, a transparent conductive film 50 of In₂O₃ is formed on the substrate 30. The transparent conductive film 50 may be formed by layering In₂ on the substrate through sputtering and then oxidizing a surface of the In₂ layer through an oxygen plasma process. At that time, the oxygen plasma is implemented under conditions of a pressure of about 5 Torr and a power of about 500 W. For the thermal annealing process, it is preferably implemented at a temperature of about 350 to 600° C. The transparent conductive film 50 of In₂O₃ is formed on the substrate 30 through lamination and surface oxidization. Then, a photoresist film is formed on the transparent conductive film 50, and then is subjected to a photolithography etching process to form a photoresist pattern 52. The substrate is etched using the photoresist pattern 52 as an etching mask to form the lower metal wiring 50a of the transparent conductive film pattern. At that time, the etching is implemented by wet etching, in which it uses an etching solution mixed with HCl and H₂O at a ratio of 1:1, and the substrate is immersed into the etching solution at about 50° C. during about 1 minute

[0034] Referring to FIG. 3D, an interlayer insulation film is formed on the substrate 30 with the lower metal wiring 50a formed thereon. At that time, an oxide film is generally selected as the interlayer insulation film. The interlayer insulation film is patterned to form an interlayer insulation film pattern 60 having a via hole. A plug 50b of tungsten is formed in the via hole of the interlayer insulation film pattern 60. Formation of the plug 50b is achieved by lamination and polishing. More specifically, after a tungsten film is formed on the interlayer insulation film pattern 60 in such a way that the tungsten is sufficiently buried in the via hole, the tungsten film is polished until a surface of the interlayer insulation film pattern 60 is exposed, thereby obtaining the plug 50b.

[0035] Referring to FIG. 3E, an upper metal wiring 50c to be connected to the plug 50b is formed on the substrate. The upper metal wiring 50c is formed by the same process as that of the lower metal wiring 50a. That is, a transparent conductive film is formed on the substrate, and then is patterned to form the upper metal wiring 50c of a transparent conductive film pattern.

[0036] As a result, a metal wiring 500 consisting of the lower metal wiring 50a, the upper metal wiring 50c, and the plug 50b connecting the wirings 50a and 50c is formed on the substrate 30.

[0037] A passivation film 62 is formed on the substrate 30 with the metal wiring 500 formed thereon. The passivation film 62 is to protect the metal wiring 500 and the devices formed on the substrate from being permeated with moisture or being scratched. At that time, an oxide film is generally selected as the passivation film 62.

[0038] Referring to FIG. 3F, a color filter 64 consisting of red, green, and blue is formed on the passivation film 62. The color filter 64 is formed through three times of lamination and three times of etching. More specifically, a layer forming red is firstly layered and etched, then a layer forming green is layered and etched, and a layer forming red is finally layered and etched.

[0039] A microlens 66 is formed on the color filter 64. At that time, the microlens 66 is formed in a semi-spherical shape so as to improve an efficiency of collecting the light.

[0040] As such, the image sensor consisting of the metal wiring 500, the color filter 64, and the microlens 66 is formed on the substrate. The metal wiring 500 can be formed on the photodiode, so that the area occupied by the photodiode can be enlarged.

[0041] With the above description, according to the present invention, the metal wiring can be formed on the photodiode, so that the area occupied by the photodiode can be easily enlarged. Therefore, an image sensor having a high resolution can be obtained by increasing a ratio of the photodiode to a pixel array.

[0042] Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.