KR100672693B1 - Manufacturing Method of CMOS Image Sensor - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a CMOS image sensor that improves light receiving characteristics by reducing the generation of metal pad particles generated during pad probing. Forming a metal pad in a pad region, forming a protective film on the entire surface of the substrate including the metal pad, selectively removing the protective film on the metal pad from the surface by a predetermined thickness to form a preliminary pad opening, the substrate Forming a first planarization layer on an active region of the substrate, forming an R, G, B color filter layer on the first planarization layer, and forming a second planarization layer on the active region of the substrate including the R, G, and B color filter layers. Forming a planarization layer, forming a microlens on the second planarization layer to correspond to the R, G, and B color filter layers, and It characterized by yirueojim including the step of forming by removing the protective film that remains on the pad region group pad opening portion.

CMOS image sensor, metal pad, micro lens, probing test

Description

Method for fabricating an COMS image sensor

1 is an equivalent circuit diagram of one pixel of a general CMOS image sensor

2 is a layout view of one pixel of a general CMOS image sensor

3A-3E are cross-sectional views of each signal line and subsequent processes of a conventional CMOS image sensor.

4A to 4E are cross-sectional views of signal lines and subsequent processes of the CMOS image sensor according to the first embodiment of the present invention;

Description of the main parts of the drawing

200 semiconductor substrate 201 insulating film

202: metal pad 203: protective film

204: photosensitive film 205: pad opening portion

206 and 210: first and second planarization layers 207, 208 and 209 color filter layers

211: microlens

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a CMOS image sensor, and more particularly, to a method for manufacturing a CMOS image sensor, in which metal pad particles generated during pad probing are reduced to improve light reception characteristics. It is about.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal, and is generally a charge coupled device (CCD) and CMOS metal (Complementary Metal Oxide Silicon) image. It is divided into Image Sensor.

In the charge coupled device (CCD), a plurality of photo diodes (PDs) for converting a signal of light into an electrical signal are arranged in a matrix form, and the photo diodes in each vertical direction arranged in the matrix form. A plurality of vertical charge coupled device (VCCD) formed between the plurality of vertical charge coupled devices (VCCD) for vertically transferring charges generated in each photodiode, and horizontally transferring charges transferred by the respective vertical charge transfer regions; A horizontal charge coupled device (HCCD) for transmitting to the sensor and a sense amplifier (Sense Amplifier) for outputting an electrical signal by sensing the charge transmitted in the horizontal direction.

However, such a CCD has a disadvantage in that the manufacturing method is complicated because the driving method is complicated, the power consumption is large, and the multi-step photo process is required. In addition, the charge coupling device has a disadvantage in that it is difficult to integrate a control circuit, a signal processing circuit, an analog / digital converter (A / D converter), and the like into a charge coupling device chip, which makes it difficult to miniaturize a product.

Recently, CMOS image sensors have attracted attention as next generation image sensors for overcoming the disadvantages of the charge coupled device. The CMOS image sensor uses CMOS technology that uses a control circuit, a signal processing circuit, and the like as peripheral circuits to form MOS transistors corresponding to the number of unit pixels on a semiconductor substrate, thereby forming the MOS transistors of each unit pixel. The device adopts a switching method that sequentially detects output. That is, the CMOS image sensor implements an image by sequentially detecting an electrical signal of each unit pixel by a switching method by forming a photodiode and a MOS transistor in the unit pixel.

The CMOS image sensor has advantages, such as a low power consumption, a simple manufacturing process according to a few photoprocess steps, by using CMOS manufacturing technology. In addition, since the CMOS image sensor can integrate a control circuit, a signal processing circuit, an analog / digital conversion circuit, and the like into the CMOS image sensor chip, the CMOS image sensor has an advantage of easy miniaturization. Therefore, the CMOS image sensor is currently widely used in various application parts such as a digital still camera, a digital video camera, and the like.

On the other hand, CMOS image sensors are classified into 3T type, 4T type, and 5T type according to the number of transistors. The 3T type consists of one photodiode and three transistors, and the 4T type consists of one photodiode and four transistors. An equivalent circuit and layout of the unit pixels of the 3T-type CMOS image sensor will be described as follows.

FIG. 1 is an equivalent circuit diagram of a general 3T CMOS image sensor, and FIG. 2 is a layout diagram illustrating unit pixels of a general 3T CMOS image sensor.

As shown in FIG. 1, a unit pixel of a general 3T CMOS image sensor includes one photodiode (PD) and three nMOS transistors T1, T2, and T3. The cathode of the photodiode PD is connected to the drain of the first nMOS transistor T1 and the gate of the second nMOS transistor T2. The sources of the first and second nMOS transistors T1 and T2 are all connected to a power supply line supplied with a reference voltage VR, and the gate of the first nMOS transistor T1 has a reset signal RST. It is connected to the reset line supplied. Further, the source of the third nMOS transistor T3 is connected to the drain of the second nMOS transistor, the drain of the third nMOS transistor T3 is connected to a read circuit (not shown in the drawing) via a signal line, The gate of the third nMOS transistor T3 is connected to a column select line to which a selection signal SLCT is supplied. Accordingly, the first nMOS transistor T1 is referred to as a reset transistor Rx, the second nMOS transistor T2 is referred to as a drive transistor Dx, and the third nMOS transistor T3 is referred to as a selection transistor Sx.

As shown in FIG. 2, in the unit pixel of a general 3T CMOS image sensor, an active region 10 is defined so that one photodiode 20 is formed in a wide portion of the active region 10. Gate electrodes 120, 130, and 140 of three transistors that overlap each other in the active region 10 of the remaining portion are formed. That is, the reset transistor Rx is formed by the gate electrode 120, the drive transistor Dx is formed by the gate electrode 130, and the selection transistor Sx is formed by the gate electrode 140. Is formed. Here, impurity ions are implanted into the active region 10 of each transistor except for lower portions of the gate electrodes 120, 130, and 140 to form source / drain regions of each transistor. Therefore, a power supply voltage Vdd is applied to a source / drain region between the reset transistor Rx and the drive transistor Dx, and a source / drain region on one side of the select transistor Sx is shown in a read circuit (not shown). Not used).

Although not illustrated in the drawings, the gate electrodes 120, 130, and 140 described above are connected to respective signal lines, and each of the signal lines has a pad at one end thereof and is connected to an external driving circuit.

As described above, each signal line including the pad and the processes proceeding thereafter are described below.

3A-3E are cross-sectional views of each signal line and subsequent process of a conventional CMOS image sensor.

First, as shown in FIG. 3A, an insulating film 101 (for example, an oxide film) such as a gate insulating film or an interlayer insulating film is formed on the semiconductor substrate 100, and the metal pads of the signal lines of the respective signal lines are formed on the insulating film 101. 102). In this case, the metal pad 102 may be formed on the same layer as the same material as each of the gate electrodes 120, 130, and 140 as described with reference to FIG. 2, and may be formed of a different material through separate contacts. It is mostly formed of aluminum (Al). A protective film 103 is formed on the entire surface of the insulating film 101 including the metal pad 102. The protective film 103 is formed of an oxide film or a nitride film.

As shown in FIG. 3B, a photosensitive film 104 is coated on the protective film 103, exposed and developed to pattern the upper portion of the metal pad 102. The protective layer 103 is selectively etched using the patterned photoresist 104 as a mask to form an open portion 105 in the metal pad 102.

As shown in FIG. 3C, the photoresist layer 104 is removed, the first planarization layer 106 is deposited on the passivation layer 103, and the portion except for the metal pad portion is formed by using a photolithography process using a mask. Only remain. A blue color filter layer 107, a green color filter layer 108, and a red color filter layer 109 are sequentially formed on the first planarization layer 106 corresponding to each photodiode region (not shown in the figure). Here, each of the color filter layer forming methods may apply the color resist and form each color filter layer by a photolithography process using a separate mask.

As shown in FIG. 3D, the second planarization layer 111 is formed on the entire surface of the substrate including the color filter layers 107, 108, and 109, and the photo-etching process using a mask remains only in an area except the metal pad portion. do.

As shown in FIG. 3E, the microlenses 112 are formed corresponding to the color filter layers 107, 108, and 109 on the second planarization layer 111.

Then, after checking the contact resistance by a probe test of each metal pad 102 of the CMOS image sensor manufactured as described above, if there is no abnormality, the external driving circuit and the metal pad are electrically connected.

However, in the conventional method of manufacturing a CMOS image sensor as described above has the following problems.

First, after the open part is formed in the metal pad, the first flattening layer formation, each color filter layer formation, the second flattening layer formation, and the microlens formation are performed. Therefore, since each subsequent process is performed while the metal pad is exposed, the metal pad is damaged by an alkali solution of TMAH series and deformed into hard aluminum due to the subsequent process. The resistance increases, which increases the failure rate during probe testing.

In addition, during the probe test, deep probing may be performed to scrape the surface of the metal pad to reduce contact resistance. In this case, a large amount of particles of the metal pad may be generated, causing the particles to paralyze the photodiode function. The yield will be reduced.

In the related art, the metal pad open part may be formed after the microlens is formed, but since the color filter layer is formed of a photosensitive material, the metal pad open part may be formed using a photolithography process after forming the micro lens. Since the color filter layer is damaged, the metal pad opening may not be formed after the microlens is formed.

The present invention is to solve the above problems, by adjusting the amount of etching of the protective film so that the metal pad is not turned off to remove only a predetermined thickness from the surface of the protective film, to reduce the contact resistance by protecting the metal pad from the post-process Furthermore, it is an object of the present invention to provide a method for manufacturing a CMOS image sensor capable of improving yield.

Method for manufacturing a CMOS image sensor according to the present invention for achieving the above object, forming a metal pad in a pad region on the substrate divided into an active region and a pad region, a protective film on the front surface of the substrate including the metal pad Forming a preliminary pad opening by selectively removing a passivation layer on the upper surface of the metal pad by a predetermined thickness from the surface; forming a first planarization layer on an active region of the substrate; Forming an R, G, B color filter layer thereon; forming a second planarization layer on an active region of the substrate including the R, G, B color filter layer; and forming the R, G, B color filter layer on the second planarization layer Forming a microlens corresponding to the color filter layer, and forming a pad opening by removing a protective film remaining in the pad region. Characterized by the yirueojim hereinafter.

Referring to the accompanying drawings, a method of manufacturing a CMOS image sensor according to the present invention having the features as described above in more detail as follows.

4A to 4E are cross-sectional views of a CMOS image sensor according to a first embodiment of the present invention.

First, as shown in FIG. 4A, an insulating film 201 such as a gate insulating film or an interlayer insulating film is formed on the semiconductor substrate 200, and metal pads 202 of each signal line are formed on the insulating film 201. In this case, the metal pad 202 may be formed on the same layer as the same material as each of the gate electrodes 120, 130, and 140 as described with reference to FIG. 2, and may be formed of a different material through a separate contact. It is mostly formed of aluminum (Al). A protective film 203 is formed on the entire surface of the insulating film 201 including the metal pad 202. The protective film 203 is formed of an oxide film or a nitride film.

As shown in FIG. 4B, a photosensitive film 204 is formed on the passivation film 203, and is exposed and developed to selectively pattern the upper portion of the metal pad 202.

Subsequently, the passivation layer 203 is selectively etched only a predetermined thickness from the surface by using the patterned photoresist 204 as a mask to form a preliminary pad opening 205a in the metal pad 202.

As shown in FIG. 4C, the photoresist layer 204 is removed, the first planarization layer 206 is deposited on the entire surface of the semiconductor substrate 200, and the metal pad portion is formed using a photolithography process using a mask. Only remain in areas except for.

A blue color filter layer 207, a green color filter layer 208, and a red color filter layer 209 are sequentially formed on the first planarization layer 206 corresponding to each photodiode region (not shown in the figure). Here, in each of the color filter layer forming methods, each color filter layer is formed by applying a photosensitive material and performing a photolithography process using a separate mask.

As shown in FIG. 4D, the second planarization layer 210 is formed on the entire surface of the substrate including the color filter layers 207, 208, and 209, and the photo-etching process using a mask remains only in the region except the metal pad portion. do.

As shown in FIG. 4E, a dielectric material is deposited on the second planarization layer 210 and selectively removed from the dielectric material by a photolithography process to correspond to each color filter layer 207, 208, and 209 of the image. The lens 211 is formed.

In this case, the pad opening 205 may be formed by selectively removing the passivation layer 203 remaining on the upper portion of the metal pad 202 by a blanket etch or the like without adding a separate mask.

Meanwhile, in the method of manufacturing the CMOS image sensor according to the first embodiment of the present invention, the pad opening part 205 is formed after the microlens 211 is formed, but the second embodiment of the present invention is performed. In the method of manufacturing a CMOS image sensor according to an example, the pad opening part 205 may be formed first, and then the microlens 211 may be formed.

After checking the contact resistance by a probe test of each metal pad 202 of the CMOS image sensor manufactured as described above, if there is no abnormality, the external driving circuit and the metal pad are electrically Connect it.

As described above, the method of manufacturing the CMOS image sensor according to the present invention has the following effects.                     

First, the protective film on the upper part of the metal pad is completely removed to form a metal pad open part, and the protective film is selectively removed only from the surface by a predetermined thickness to form a preliminary open part on the upper part of the metal pad. It is possible to reduce the contact resistance of the metal pad by preventing the pad from corrosion.

Second, since the contact resistance of the metal pad is reduced as described above, the photodiode function caused by the metal pad particles is paralyzed since there is no need to perform deep probing to scrape the surface of the metal pad during the probe test. You can prevent it.

Claims (5)

Forming a metal pad in a pad area on the substrate divided into an active area and a pad area; Forming a protective film on an entire surface of the substrate including the metal pads; Selectively removing the passivation layer on the metal pad by a predetermined thickness from a surface to form a preliminary pad opening; Forming a first planarization layer on the active region of the substrate; Forming an R, G, B color filter layer on the first planarization layer; Forming a second planarization layer on the active region of the substrate including the R, G, B color filter layers; Forming a micro lens on the second planarization layer to correspond to the R, G, and B color filter layers; And And forming a pad opening by removing the protective film remaining in the pad region. The method of claim 1, wherein an insulating film is further formed between the substrate and the metal pad. The method of claim 1, wherein the metal pad is formed of aluminum. The method of claim 1, wherein the pad opening is formed by blanket etching the passivation layer. delete

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