KR20060077129A - Image sensor with enhanced optical sensitivity - Google Patents

Abstract

The present invention is to provide an image sensor that can prevent a decrease in light sensitivity due to a structural problem including a multilayer metal line of the image sensor and an insulating film therebetween, and to improve the light sensitivity. A photodiode provided on the substrate; A microlens disposed above the photodiode so as to overlap the photodiode; And a reflective wall disposed around the light passage leading from the microlens to the photodiode.

The present invention also provides a photodiode provided on a substrate; A plurality of metal lines disposed on the photodiode and interconnected through a plurality of via contacts; And a microlens disposed on the plurality of metal lines so as to overlap the photodiode, wherein the plurality of via contacts form a reflective wall around a light path leading from the microlens to the photodiode. Provide an image sensor.

Reflective walls, via contacts, metal lines, image sensors, light paths.

Description

Image sensor with improved light sensitivity {IMAGE SENSOR WITH ENHANCED OPTICAL SENSITIVITY}             

1 is a cross-sectional view schematically showing a conventional image sensor.

2 is a cross-sectional view showing a CMOS image sensor according to an embodiment of the present invention.

3 schematically illustrates an image sensor with a reflective wall according to another embodiment of the invention.

4 is a view illustrating that light is reflected from a reflective wall having the structure of FIG. 3 and incident to a photodiode;

Explanation of symbols on the main parts of the drawings

SUB: Substrate Fox: Field Oxide

PMD: Insulation film before metal line formation M1 to M4: Metal line

IMD1 to IMD3: Insulation between metal lines PL: Protective film

OCL: Overcoat Layers V1 to V4: Via Contacts

CFA: Color Filter Array ML: Micro Lens

PSL: Shield

The present invention relates to an image sensor, and more particularly, to an image sensor having improved light sensitivity.

CMOS image sensors are devices widely used in mobile phones, cameras for personal computers (PCs), and electronic devices. CMO image sensor is simpler to drive than CCD (Charge Coupled Device) which is used as image sensor, and it is possible to integrate signal processing circuit into one chip so that SOC (System On Chip) is possible. Allows the module to be miniaturized.

In addition, since the conventional set-up CMOS technology can be used interchangeably, it has many advantages, such as lowering the manufacturing cost.

1 is a cross-sectional view showing unit pixels of a CMOS image sensor arranged so that all RGB colors appear.

Referring to FIG. 1, a field oxide film FOX is formed locally on a substrate SUB having a structure in which a high concentration of P-type (P ++) region and an epi layer (P-epi) are stacked, and on the substrate SUB. A plurality of gate electrodes including a transfer gate (not shown) are formed, for example, an N-zero region (not shown) by deep ion implantation under the surface of the substrate SUB aligned on one side of the transfer gate; A photodiode PD formed of a P-type region (not shown) is formed in a region in contact with the surface of the substrate SUB. Although not shown in the drawing, in this case, a highly concentrated N-type (N +) floating diffusion region is formed under the surface of the substrate SUB aligned on the other side of the transfer gate by ion implantation.

The pre-metal dielectric (hereinafter referred to as PMD) is formed on the entire surface of the photodiode PD and the transfer gate, and the first metal line M1 is formed on the PMD.

An inter-metal dielectric (hereinafter, referred to as IMD1) is formed on the first metal line M1, and a second metal line M2 is formed on the IMD1. A second intermetallic insulating film IMD2 is formed on the second metal line M2, and a third metal line M3 is formed on the IMD2. The third intermetallic insulating film IMD3 is formed on the third metal line M3, and the fourth metalline M4 is formed on the IMD3.

The first to fourth metal lines M1 to M4 are used to connect power lines, signal lines, unit pixels, and logic circuits, and serve as a shield to prevent light from being incident on a region other than the photodiode PD. At the same time.

In addition, although the fourth metal line M4 is shown as a final metal line, the fourth metal line M4 may include a fifth or sixth metal line or more.

A passivation layer (hereinafter referred to as PL) is formed on the fourth metal line M4, and a color filter array for implementing RGB color for each unit pixel is formed on the PL. (Hereinafter referred to as CFA).

Here, the PL generally includes a double structure of a nitride film / oxide film and a planarization film (over coating layer) (hereinafter referred to as OCL) for securing a process margin when forming CFA.

R (Red) G (Green) B (Blue), which is the three primary colors of ordinary light, is used. In addition, yellow, magenta (Mg), and cyan (Cy), which are complementary colors, may be used. .

A planarization film (hereinafter referred to as OCL) is formed on the CFA to secure process margins when forming the microlens, and a microlens (hereinafter referred to as ML) is formed on the OCL.

On the ML, a protective film (hereinafter referred to as PSL) is formed to prevent the ML from being scratched or broken. The incident light is focused by the microlens ML and enters the photodiode PD.

In order to manufacture a CMOS image sensor as shown in FIG. 1, a PD is formed, a required metal line is formed thereon, then a CFA is formed, and the step generated by the CFA is removed by forming an OCL.

The ML forming photoresist is applied onto the OCL to form the ML, and then the thermal process causes the photoresist to be in a semi-liquid state. At this time, the photoresist forms a convex ML by surface tension, and forms a low temperature oxide (LTO) film by chemical vapor deposition (CVD) on the ML using PSL.

As shown, a metal line of M1 to M4 and a plurality of insulating films PMD, PL, and IMD1 to IMD3 are included between the photodiode PD and the color filter array CFA.

As such, as the number of metal lines increases, the distance from the ML to the photodiode PD increases. Therefore, it is highly likely that the focal point of the ML is not formed on the surface of the photodiode PD but is formed in the middle or out of the photodiode PD. Reference numeral 'X' indicates that light incident from the ML is not transmitted to the photodiode PD.

When this phenomenon occurs, the loss of light occurs and the amount of current generated by the photodiode PD is reduced, so that a clear image cannot be obtained.

The present invention proposed to solve the problems of the prior art, it is possible to prevent the optical sensitivity degradation due to the structural problems including the multilayer metal line of the image sensor and the insulating film therebetween, and can improve the optical sensitivity The purpose is to provide an image sensor.

In order to achieve the above object, the present invention, a photodiode provided on the substrate; A microlens disposed above the photodiode so as to overlap the photodiode; And a reflective wall disposed around the light passage leading from the microlens to the photodiode.

The present invention also provides a photodiode provided on a substrate; A plurality of metal lines disposed on the photodiode and interconnected through a plurality of via contacts; And a microlens disposed on the plurality of metal lines so as to overlap the photodiode, wherein the plurality of via contacts form a reflective wall around a light path leading from the microlens to the photodiode. Provide an image sensor.

In order to solve the problem that the light incident from the microlens does not reach the photodiode and enters another place, the present invention uses a via contact and a metal line to form a reflective wall made of metal around the passage through which the light is transmitted.

Therefore, even if the light injected through the microlenses is not transmitted to the photodiode and the direction is changed, the light may be reflected from the metal reflective wall and transmitted to the photodiode.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.                     

2 is a cross-sectional view illustrating a CMOS image sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the CMOS image sensor of the present invention includes a plurality of field oxide films (hereinafter referred to as Fox) disposed locally on a substrate SUB, a photodiode PD provided on a substrate SUB between Foxes, A plurality of transistors (not shown) disposed on the substrate SUB, an insulating film before forming metal lines (hereinafter referred to as PMD) disposed on the photodiode PD, a source / drain of the transistor through the PMD, or A via contact connected to the gate electrode (hereinafter referred to as V1), a first metal line connected to V1 (hereinafter referred to as M1), an interlayer insulating film (hereinafter referred to as IMD1) disposed on M1, A second via contact connected to M1 through IMD1 (hereinafter referred to as V2), a second metal line connected to V2 (hereinafter referred to as M2), and an insulating film between a second metal line disposed on M2 (hereinafter referred to as IMD2). A third via contact (hereinafter referred to as V3) connected to M2 through IMD2, and a third metalline (hereinafter referred to as V3) connected to V3. M3), a third intermetallic insulating film (hereinafter referred to as IMD3) disposed on M3, a fourth via contact (hereinafter referred to as V4) connected to M3 through IMD3, and a second connected to V4. 4 metal line (hereinafter referred to as M4), a protective film (hereinafter referred to as PL) disposed on M4, a color filter array (hereinafter referred to as CFA) arranged on the PL, an OCL arranged on the CFA, and an OCL A microlens (hereinafter referred to as ML) disposed to overlap with the photodiode PD on it, and a protective film (hereinafter referred to as PSL) disposed on the ML to prevent the ML from being scratched or broken.

Here, the transistor includes a reset transistor, a drive transistor, a select transistor, and the like, and in the case of a structure including four transistors, the transistor may further include a transfer transistor.                     

V1 to V4 form a reflective wall of metal around the light path from ML to PD. The metal used as the material of V1 to V4 includes W, Ti, TiN, or Al.

Although M4 is shown as the final metal line here, there are also cases in which more metal lines such as the seventh or eighth are included.

R (Red) G (Green) B (Blue), which is the three primary colors of ordinary light, is used. In addition, yellow, magenta (Mg), and cyan (Cy), which are complementary colors, may be used. .

Here, the substrate SUB has a structure in which a high concentration P-type (P ++) region and an epi layer (P-epi) are stacked, and the photodiode PD is formed by deep ion implantation under the surface of the substrate SUB. It consists of a zero area (not shown) and a P-type area (not shown) located in an area in contact with the surface of the substrate SUB.

Through the above structure, the present invention solves the problem that light incident from the ML is incident to a place other than the PD before being transmitted to the PD.

When forming V1-V4 and M1-M4, a reflective wall of V1-V4 is formed around the passage through which light is transmitted. That is, after the trench is formed around the PD in the via forming step, the via contact forming process is performed, so that the metal filled in the trench, that is, V1 to V4, surrounds the PD.

When the metal line is formed after the via contact is formed, the reflective fence is formed of the metal for the metal line along the via trench formed around the PD. At this time, the alignment of the via trench with the metal fence is preferable to allow the fence to enter the PD slightly further.

That is, as shown in the right side of Figure 2, the via trench formed in the next layer also induces misalignment (Mis-alignment) to be located inside the PD rather than the lower fence.

This method is repeatedly carried out to form a reflective wall (fence) made of metal consisting of V1 to V4 and M1 to M4 around the PD.

The advection that shifts the via trench or fence alignment towards the area occupied by the lower PD toward the upper layer is such that the light reflected by the metal reflective wall can be directed towards the lower PD.

If the lower fences or via trenches are aligned to the PD side more than the upper side, if the light hits this part, they will be reflected out and cannot reach the PD surface. Therefore, when the width of the reflective wall is narrowed toward the upper side, incident light having a different direction is reflected by the metal reflective wall and reaches the PD for various reasons, so that an image of excellent quality can be obtained.

3 is a schematic view of an image sensor having a reflective wall according to another embodiment of the present invention.

Referring to FIG. 3, PD is disposed at a lower portion, and metal lines of M1 to M4 are stacked on the upper portion. M1 to M4 are interconnected between the upper and lower portions through the via contact V, and the via contact V forms a reflective wall around the light path from the ML (not shown) to the PD.                     

In this case, the via contact V itself may form a reflective wall, and a metal pattern additionally inserted such as the via contact V may form a reflective wall.

FIG. 4 is a diagram illustrating that light is reflected from a reflective wall having the structure of FIG. 3 and incident to a photodiode.

As such, by forming a reflective wall around the optical path using the metal, the light collecting efficiency of the photodiode can be increased.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

For example, in the above-described embodiment of the present invention, the CMOS image sensor is taken as an example, but it is also applicable to all image sensors having the light receiving unit and the microlens.

According to the present invention described above, light having a high probability of loss can be incident on the photodiode through the reflective wall disposed in the light path to increase the light sensitivity, thereby improving the image quality of the image sensor.

Claims (6)

A photodiode provided on the substrate; A microlens disposed above the photodiode so as to overlap the photodiode; And Reflective wall disposed around the light path leading from the microlens to the photodiode Image sensor comprising a. The method of claim 1, The reflecting wall is an image sensor, characterized in that the width becomes narrower toward the top. The method according to claim 1 or 2, The reflective wall is an image sensor, characterized in that the metal material. A photodiode provided on the substrate; A plurality of metal lines disposed on the photodiode and interconnected through a plurality of via contacts; And A microlens disposed on the plurality of metal lines so as to overlap with the photodiode, And the plurality of via contacts form a reflective wall around a light path leading from the microlens to the photodiode. The method of claim 4, wherein The reflecting wall is an image sensor, characterized in that the width becomes narrower toward the top. The method according to claim 4 or 5, The via contact includes any one of Ti, TiN, W or Al.

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