KR20050067524A - Cmos image sensor with local light shield metal - Google Patents

Abstract

The present invention relates to a CMOS image sensor, and in particular, by constructing a light blocking layer using a plurality of local metals rather than a conventional global metal, thereby reducing the influence of noise generated in adjacent blocks. to be. To this end, in the present invention, each local light blocking layer is separately provided on each block except the light receiving unit among the plurality of blocks constituting the CMOS image sensor. The noise effect between adjacent blocks is reduced.

Description

CMOS image sensor with local light blocking layer {CMOS IMAGE SENSOR WITH LOCAL LIGHT SHIELD METAL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CMOS image sensor, and in particular, by using several local metals as light blocking layers, the present invention solves the problems of the prior art of using one global metal as a light blocking layer. .

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. Among them, a charge coupled device (CCD) includes individual metal-oxide-silicon (MOS) capacitors. A device in which charge carriers are stored and transported in a capacitor while being in close proximity to each other. Complementary MOS image sensors use CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. A device employing a switching scheme that creates MOS transistors as many as pixels and sequentially detects outputs using the MOS transistors.

FIG. 1A is a circuit diagram illustrating a unit pixel including one photo diode and four MOS transistors in a conventional CMOS image sensor, and includes a photodiode 100 that generates photocharges by receiving light. A transfer transistor 101 for transporting the photocharges collected in the photodiode by receiving the Tx signal to the gate to the floating diffusion region (FD) 102 and the floating diffusion to the desired value by receiving the Rx signal to the gate A reset transistor 103 for setting the potential of the region 102 and discharging the charge to reset the floating diffusion region 102 and a Dx signal applied to the gate serves as a source follower buffer amplifier. Drive transistor 104 and a select transistor (Sx) that receives the Sx signal to the gate (Switching) addressing (Switching) to enable addressing (Switching) It is. Outside the unit pixel, a load transistor 106 is formed to read an output signal.

The CMOS image sensor is composed of a light receiving unit composed of tens or millions of unit pixels shown in FIG. 1A and a peripheral circuit unit which converts and processes an electrical signal generated by using light into an electrical signal necessary for image reproduction. 1b is a block diagram showing an entire CMOS image sensor composed of these various blocks.

Referring to FIG. 1B, the CMOS image sensor includes a light receiver 13 for receiving light and converting the light into an electrical signal, and first to third analog circuits 14 and 15 for processing an analog signal which is an output signal of the light receiver. 16) and first to second digital circuit parts 11 and 12 for processing the digital signal changed from the analog signal to the digital signal.

In the CMOS image sensor having such a structure, the incoming light is introduced into not only the light receiving unit 13 but also the analog circuit units 14, 15 and 16 and the digital circuit units 11 and 12, and the light incident to an area other than the light receiving unit 13. The silver may not only raise the temperature but also form an electron hole pair (EHP) to have a different characteristic from the model characteristic at the time of design, thereby causing malfunction.

FIG. 1C illustrates a state in which a light blocking layer is applied to block light incident to an area other than the light receiving unit. In the related art, light incident to an area other than the light receiving unit is used by using a single global metal. I prevented it.

That is, the entire region except for the light receiving unit 13 is covered with one global metal 17 and the light is blocked by using the same. Hereinafter, such a light blocking layer will be referred to as a global light shielding metal.

Such a global light shielding layer was able to achieve the original purpose of blocking light well, but had the following disadvantages. That is, the noise component generated in the adjacent block is transmitted to the adjacent block through the global light blocking layer, which may adversely affect the overall circuit operation, and the noisy ground power of the digital circuit portion shakes the quiet ground voltage of the analog circuit portion. This may cause power noise in the analog circuit section.

An object of the present invention is to provide a CMOS image sensor that reduces the influence of noise by forming a light blocking layer for each block of local metal layers instead of one global metal layer.

The present invention for achieving the above object is a CMOS sensor comprising a light receiving portion, an analog circuit portion and a digital circuit portion, wherein the analog circuit portion is composed of a plurality of sub-circuit portion, the digital circuit portion is composed of a plurality of sub circuit portion And a plurality of local light blocking layers respectively covering the plurality of sub circuit units.

The present invention also provides a CMOS sensor comprising a light receiving unit, an analog circuit unit and a digital circuit unit, comprising: a first local light blocking layer covering only the analog circuit unit; And a second local light blocking layer covering only the digital circuit portion.

The present invention reduces the influence of noise by forming a light blocking layer for each block using a plurality of local metal layers.

Hereinafter, the most preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily implement the technical idea of the present invention.

FIG. 2 is a plan view showing a case in which a light blocking layer is formed by using a block arrangement and a local metal layer of a CMOS image sensor according to an exemplary embodiment of the present invention, with reference to this. FIG.

Referring to FIG. 2, the CMOS image sensor according to an exemplary embodiment of the present invention includes a light receiving unit 13 that receives electric light and generates an electrical signal, and an analog circuit unit 14, 15, which processes an analog signal generated by the light receiving unit. 16), and digital circuit units 11 and 12 for processing digital signals converted from analog signals to digital signals, and local light blocking layers 20, 21, 22, and 23 separately configured for each block to block light. , 24). The local light blocking layer used as the light blocking layer is a metal layer which is located at the top layer and is not used for wiring purposes.

In one embodiment of the present invention, the entire digital circuit portion is composed of two sub circuit portions of the first digital circuit portion 11 and the second digital circuit portion 12, and the entire analog circuit portion 14 is composed of the first analog circuit portion 14. And three sub circuit portions of the second analog circuit portion 15 and the third analog circuit portion 16.

The number of sub-circuit units of the digital circuit unit or the analog circuit unit may be modified as much as the purpose of the image sensor or the intention of the designer. However, in an embodiment of the present invention, the digital circuit unit may include two digital circuit units. It is said that it consists of a sub circuit part, and the analog circuit part consists of three sub circuit parts.

2, local light blocking layers 20, 21, 22, 23, and 24 covering respective circuit blocks except for the light receiving unit are illustrated. For example, the local light blocking layer formed on the first digital circuit portion 11 is denoted by '20', and the local light blocking layer formed on the third analog circuit portion 16 is denoted by the numeral '24'.

Thus, in one embodiment of the present invention by forming a local light blocking layer on each block except for the light receiving unit 13 of each block constituting the CMOS image sensor, in addition to the natural effect of blocking light, adjacent blocks We solved the problem that noise influences each other.

Each of the local light blocking layers 20, 21, 22, 23, and 24 is connected to ground power so that the local light blocking layer is not in a floating state.

In addition, since the portion of each block affected by the light energy is a transistor, a capacitor, a resistor, etc., only the corresponding device needs to be blocked from the light energy. In general, the metal layer used as the signal transmission line is affected by the light energy. It does not need to be covered with a light blocking layer.

In view of this point, the local light blocking layer shielding each sub circuit part may be laid out so as to shield only the device affected by light, or the entire sub circuit part may be covered with the local light blocking layer.

In an embodiment of the present invention, although the local light blocking layer is formed on each of the sub-circuits except for the light receiving unit among the blocks constituting the CMOS image sensor, the local light blocking layer may be formed for each block having the same electrical characteristics. It may be.

That is, in FIG. 2, since the electrical characteristics of the analog circuit portions 14, 15, 16 and the digital circuit portions 11, 12 are very different from each other, the entire analog circuit portions 14, 15, and 16 are blocked in one local light. Layer, and the entire digital circuit portion 11, 12 may be covered with another local light shielding layer.

This is because electrical influences between blocks having very different electrical characteristics become a big problem in circuit operation, while electrical influences between the same analog circuit portion or the same digital circuit portion are insignificant.

Of course, if the local light blocking layer is formed for each sub-circuit unit as in the embodiment of the present invention, it is possible to prevent even the effect of noise between adjacent blocks can achieve a more excellent effect.

As described above, the present invention is not limited to the above-described embodiments and the accompanying drawings, and the present invention may be variously substituted, modified, and changed without departing from the spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

Application of the present invention to the CMOS image sensor can reduce the effect between adjacent blocks as well as light blocking can improve the characteristics of the device.

1A is a circuit diagram showing the configuration of unit pixels in a CMOS image sensor of the prior art;

Figure 1b is a block diagram of the CMOS image sensor according to the prior art,

Figure 1c is a plan view showing a state of covering the CMOS image sensor with a global light blocking layer according to the prior art,

Figure 2 is a plan view showing a state that covers the CMOS image sensor with a local light blocking layer according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

11: first digital circuit portion

12: second digital circuit portion

13: light receiver

14: first analog circuit portion

15: second analog circuit portion

16: third analog circuit portion

17: global light blocking layer

20, 21, 22, 23, 24: local light blocking layer

Claims (8)

In the CMOS sensor comprising a light receiving unit, an analog circuit unit and a digital circuit unit, The analog circuit portion is composed of a plurality of sub circuit portions, the digital circuit portion is composed of a plurality of sub circuit portions, and a plurality of local light blocking layers respectively covering the plurality of sub circuit portions. CMOS image sensor, characterized in that consisting of. The method of claim 1, The plurality of local light blocking layer is CMOS image sensor, characterized in that connected to the ground voltage. The method of claim 1, The plurality of local light blocking layer, CMOS image sensor, characterized in that the uppermost metal layer is not used for wiring. The method of claim 1, The local light blocking layer, A CMOS image sensor, wherein the CMOS image sensor is arranged to shield only transistors, capacitors, and resistors from light. In the CMOS sensor comprising a light receiving unit, an analog circuit unit and a digital circuit unit, A first local light blocking layer covering only the analog circuit portion; And One second local light blocking layer covering only the digital circuit portion CMOS image sensor, characterized in that consisting of. The method of claim 5, And the first local light blocking layer and the second local light blocking layer are connected to a ground voltage. The method of claim 5, The first and second local light blocking layer, CMOS image sensor, characterized in that the uppermost metal layer is not used for wiring. The method of claim 5, The first and second local light blocking layer, A CMOS image sensor, wherein the CMOS image sensor is arranged to shield only transistors, capacitors, and resistors from light.