CN108598100A - A kind of global pixel structure and production method reducing memory node light leakage - Google Patents

Abstract

The invention discloses a global pixel structure for reducing light leakage of a storage node, which includes a photodiode, a transfer transistor and a reset transistor arranged on a substrate, and a photodiode formed on the substrate between the transfer transistor and the reset transistor. storage node; wherein, the transmission tube, the reset tube and the storage node are covered with a metal masking layer, the storage node is connected with a contact hole, and the contact hole is set through the metal masking layer, and is connected to the metal A gap is formed between the masking layers, and the gap is filled with an insulating reflective layer, so that the light leakage gap between the metal masking layer and the contact hole is filled with the insulating reflective layer, thus ensuring that incident light cannot enter the charge storage area of the storage node, The light leakage problem of the storage node of the global pixel unit of the CMOS image sensor is reduced, and the electrical isolation between the metal masking layer and the contact hole is guaranteed at the same time. The invention also discloses a manufacturing method of the global pixel structure for reducing the light leakage of the storage node.

Description

A global pixel structure and manufacturing method for reducing light leakage of storage nodes

technical field

The present invention relates to the technical field of CMOS image sensors, and more particularly, relates to a global pixel structure and a manufacturing method of a CMOS image sensor capable of reducing light leakage of storage nodes.

Background technique

An image sensor refers to a device that converts optical signals into electrical signals. Generally, large-scale commercial image sensor chips include charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) image sensor chips.

Compared with traditional CCD sensors, CMOS image sensors have the characteristics of low power consumption, low cost, and compatibility with CMOS technology, so they are more and more widely used. Now CMOS image sensors have not only been used in the field of consumer electronics, such as miniature digital cameras (DSC), mobile phone cameras, video cameras and digital single-lens reflex cameras (DSLR), but also in automotive electronics, monitoring, biotechnology and medicine. application.

The pixel unit of a CMOS image sensor is the core device for the image sensor to realize light sensing. The most commonly used pixel unit is an active pixel structure including a photodiode and four transistors. In these devices, the photodiode is a photosensitive unit, which realizes light collection and photoelectric conversion; other MOS transistors are control units, which mainly realize the control of photodiode selection, reset, signal amplification and readout. The number of MOS transistors in a pixel unit determines the area occupied by the non-photosensitive area. The above-mentioned pixel structure including four transistors is generally called a 4T pixel unit.

There are usually two kinds of shutter control modes in digital cameras: the mechanical shutter and the electronic shutter. The mechanical shutter controls the exposure time by opening and closing the mechanical parts installed in front of the CMOS image sensor; the electronic shutter changes the integration time through the timing control of the pixel unit, so as to achieve the purpose of controlling the exposure time. Because the mechanical shutter needs mechanical parts, it will occupy the area of the digital camera, so it is not suitable for portable digital cameras. For video surveillance applications, since video acquisition is usually performed, an electronic shutter is generally used to control the exposure time. Among them, the electronic shutter is divided into two types: the rolling shutter type and the global exposure type. The exposure time between each line of the rolling shutter electronic shutter is inconsistent, which is easy to cause smear phenomenon when shooting high-speed objects; while each line of the global exposure electronic shutter is exposed at the same time, and then the charge signal is stored in the pixel at the same time The storage node of the unit, and finally output the signal of the storage node row by row. Global exposure type electronic shutter does not cause smear phenomenon because all lines are exposed at the same time.

With the increasing application of CMOS image sensors in industry, vehicles, road monitoring and high-speed cameras, the demand for image sensors that can capture images of high-speed moving objects has further increased. In order to monitor high-speed objects, CMOS image sensors need to use globally exposed pixel units (referred to as global pixels), and the storage nodes used to store charge signals in globally exposed pixel units are a very important indicator of the parasitic response to light sources. In practical applications, according to the number of transistors used in each pixel unit, there are 4T, 5T, 6T, 8T, and 12T pixel units for global exposure.

Please refer to FIG. 1 . FIG. 1 is an existing layout structure of a 5T global exposure pixel unit. As shown in FIG. 1 , the charge storage node 12 in the 5T global exposure pixel unit is the junction capacitance between the transfer transistor 11 and the reset transistor 13 . The parasitic light response of the storage node refers to the parasitic response of the storage node capacitance due to light leakage. For the pixel unit, the light incident on the surface of the pixel unit cannot be fully focused on the surface of the photodiode 10 due to refraction and scattering, and some light may Incident to the storage node 12, the storage node 12 can also generate a photoelectric response like the photodiode 10 under the irradiation of the incident light. The charge generated on the storage node 12 due to the irradiation of incident light will affect the voltage signal originally stored on the storage node 12 and generated by the photodiode 10 , resulting in signal distortion. In order to reduce the parasitic response of the light source of the storage node, it is necessary to use a completely opaque metal shielding layer on the storage node to prevent the influence of incident light.

Please refer to FIG. 2 . FIG. 2 is a cross-sectional view of the global pixel structure along the direction A-B in FIG. 1 . As shown in FIG. 2 , compared with the common CMOS process, in order to prevent the parasitic photoresponse of the global pixel unit, the conventional global pixel unit is provided with an additional layer of metal masking layer 17 formed in the interlayer dielectric 16 . The metal masking layer 17 is usually made of opaque metals such as tungsten, aluminum and copper, or metal compound materials such as tantalum nitride and tantalum nitride. Since the metal masking layer 17 covers the transmission tube 11, the reset tube 13, and the storage node 12 in a large area, in order to avoid crosstalk between the transmission tube 11, the reset tube 13, and the storage node 12 during the operation of the pixel, all the metal masking layers 17 pass through The metal interconnection is finally grounded; meanwhile, the storage node 12 is connected to the metal interconnection layer 14 through the contact hole 15 .

In the above global pixel structure, since the storage node 12 is a constantly changing dynamic signal during operation, the contact hole 15 on the storage node 12 and the metal mask layer 17 cannot be connected, but must maintain a certain distance. Thus, a light leakage gap 18 is formed on the storage node 12 . The position of the light leakage gap 18 is not covered by the metal masking layer 17 or the contact hole 15, so the incident light can directly pass through the light leakage gap 18 to reach the storage node 12, resulting in distortion of the global pixel storage signal and degradation of image quality.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and provide a global pixel structure and a manufacturing method for reducing light leakage of storage nodes.

To achieve the above object, the technical scheme of the present invention is as follows:

The present invention provides a global pixel structure for reducing light leakage of storage nodes, including a photodiode, a transfer transistor and a reset transistor arranged on a substrate, and a photodiode formed on the substrate between the transfer transistor and the reset transistor A storage node; wherein, the transmission tube, the reset tube and the storage node are covered with a metal masking layer, the storage node is connected with a contact hole, the contact hole is set through the metal masking layer, and is connected to the metal A gap is formed between the masking layers, and the gap is filled with an insulating reflective layer.

Further, the insulating reflective layer is a composite insulating reflective layer structure formed by stacking multiple layers of insulating media.

Further, the refractive index between any two adjacent layers of insulating media in the composite insulating reflective layer is different.

Further, the materials between any two adjacent layers of insulating media in the composite insulating reflective layer are different.

Further, the metal masking layer is a single-layer structure or a multi-layer composite structure.

The present invention also provides a method for making a global pixel structure that reduces light leakage of storage nodes, including the following steps:

providing a substrate, forming a photodiode, a transfer transistor, and a reset transistor on the substrate, and forming a storage node on the substrate between the transfer transistor and the reset transistor;

Depositing a metal masking layer material on the surface of the substrate, removing the metal masking layer material above the photodiode, and forming an opening in the metal masking layer above the storage node to form a metal masking layer;

Depositing an insulating reflective layer material on the surface of the substrate to fill the opening of the metal masking layer, and forming an insulating reflective layer pattern above the storage node, so that the size of the insulating reflective layer pattern is larger than the size of the opening of the metal masking layer;

Depositing an interlayer dielectric on the entire surface of the substrate to form a contact hole pattern passing through the insulating reflection layer pattern and connecting the storage nodes;

The contact hole is filled, the contact hole is formed, and the subsequent metal interconnection layer connecting the contact hole is formed.

Further, the substrate is an N-type or P-type silicon substrate.

Further, the metal masking layer is a single-layer structure or a multi-layer composite structure formed of one or more of titanium, titanium nitride, tungsten, aluminum, copper, cobalt and nickel.

Further, the insulating reflective layer is a composite insulating reflective layer structure formed by stacking at least two of silicon nitride, silicon dioxide, silicon oxynitride, and nitrogen-containing silicon carbide.

Further, the material or refractive index of any two adjacent layers in the composite insulating reflective layer is different.

It can be seen from the above technical scheme that the present invention inserts an insulating reflective layer between the metal masking layer and the contact hole of the conventional global pixel unit, so that the light leakage gap between the metal masking layer and the contact hole is filled with the insulating reflective layer, And by stacking more than two layers of insulating dielectric films with different materials or refractive indices to form a composite insulating reflective layer, the incident light is reflected, thus ensuring that the incident light cannot enter the charge storage area of the storage node, reducing the overall size of the CMOS image sensor. The light leakage problem of the pixel unit storage node ensures the electrical isolation between the metal masking layer and the contact hole, thereby effectively ensuring the accuracy of the signal in the global exposure pixel unit storage capacitor, avoiding the distortion of the output signal, and making the image sensor finally High-quality images can be obtained.

Description of drawings

FIG. 1 is a schematic diagram of a layout structure of an existing 5T global exposure pixel unit;

Fig. 2 is a cross-sectional view of the global pixel structure along the A-B direction in Fig. 1;

3 is a schematic diagram of a global pixel structure for reducing light leakage of storage nodes according to a preferred embodiment of the present invention;

4-12 are schematic diagrams of process steps of a method for manufacturing a global pixel structure that reduces light leakage of storage nodes according to a preferred embodiment of the present invention.

Detailed ways

The specific embodiment of the present invention will be further described in detail below in conjunction with the accompanying drawings.

It should be noted that, in the following specific embodiments, when describing the embodiments of the present invention in detail, in order to clearly show the structure of the present invention for the convenience of description, the structures in the drawings are not drawn according to the general scale, and are drawn Partial magnification, deformation and simplification are included, therefore, it should be avoided to be interpreted as a limitation of the present invention.

In the following specific implementation manner of the present invention, please refer to FIG. 3 . FIG. 3 is a schematic diagram of a global pixel structure for reducing light leakage of storage nodes in a preferred embodiment of the present invention. As shown in FIG. 3 , a global pixel structure for reducing light leakage of a storage node in the present invention includes a photodiode 21, a transfer transistor 23 and a reset transistor 27 arranged on a substrate 20, and a photodiode 21 formed on the transfer transistor 23 and a reset transistor 27. Storage nodes 29 on substrate 20 between tubes 27 . Wherein, the charge storage node 29 is the junction capacitance between the transfer transistor 23 and the reset transistor 27 . An interlayer dielectric 22 may be disposed on the substrate 20; the interlayer dielectric 22 covers the transmission tube 23 and the reset tube 27 therein.

See Figure 3. A metal masking layer 24 is provided in the interlayer dielectric 22 ; the metal masking layer 24 covers the transmission tube 23 , the reset tube 27 and the storage node 29 .

A contact hole 25 is connected to the storage node 29 ; the contact hole 25 is disposed through the metal mask layer 24 and forms a gap 30 with the metal mask layer 24 . This gap 30 constitutes the light leakage gap between the metal mask layer 24 and the contact hole 25 on the storage node 29 in the conventional global pixel unit (please refer to the light leakage gap 18 in FIG. Incident light enters the charge storage region of the storage node 29 through the light leakage gap 30 .

Please continue with Figure 3. Since there is no electrical connection between the metal masking layer 24 and the contact hole 25 of the global pixel unit, conventional metal layers cannot be used in the light leakage gap 30 to shield incident light. In the present invention, incident light is isolated by filling (or inserting or embedding) the insulating reflective layer 28 in the gap 30 .

The insulating reflective layer 28 may be a composite insulating reflective layer 28 structure formed by stacking multiple layers of insulating media. Conventional single-layer insulating media are usually light-transmitting, but at the same time, stacking multiple insulating dielectric films can reflect most of the incident light. The reflection of the incident light by the composite insulating dielectric film depends on the difference in the refractive index between the dielectric films. The greater the difference in the refractive index of the two dielectric films, the higher the reflectivity of the incident light. For example, the use of silicon nitride film and oxide When the film is used, the difference in refractive index between the two is relatively large, and the composite film formed by them can greatly reflect the incident light. Other insulating dielectric films such as silicon carbide and silicon oxynitride can also be used.

Therefore, the refractive index between any two adjacent layers of insulating media in the composite insulating reflective layer 28 is different. Alternatively, the materials between any two adjacent layers of insulating media in the composite insulating reflective layer 28 are different. By stacking several insulating films with different refractive indices or different materials, the incident light can be greatly reflected and the light leakage problem existing in the global pixel storage node 29 can be reduced.

After the composite insulating reflective layer 28 is inserted in the light leakage gap 30 between the metal mask layer 24 and the contact hole 25 of the conventional global pixel unit, not only most of the incident light is reflected in the composite insulating layer, but also the storage node 29 is guaranteed Electrical isolation between the contact hole 25 and the metal masking layer 24.

The metal masking layer 24 can use an opaque metal or metal compound to form a single-layer structure or a multi-layer composite structure. Metal masking layer 24 may ultimately be grounded through a metal interconnect layer. The storage node 29 may be connected to the metal interconnection layer 26 through the contact hole 25 . The contact hole 25 is also filled with an opaque metal.

The above-mentioned structure of the present invention can be used in various global pixel structures requiring storage capacitors such as 4T, 5T, 6T, 8T and 12T.

A method for manufacturing a global pixel structure that reduces light leakage of storage nodes according to the present invention will be described in detail below through specific implementation methods and accompanying drawings.

Please refer to FIG. 4-FIG. 12. FIG. 4-FIG. 12 are schematic diagrams of process steps of a manufacturing method of a global pixel structure that reduces light leakage of storage nodes according to a preferred embodiment of the present invention. As shown in Figures 4-12, a manufacturing method of the global pixel structure for reducing light leakage of storage nodes according to the present invention can be used to manufacture the above-mentioned global pixel structure for reducing light leakage of storage nodes, and may include the following steps:

As shown in FIG. 4 , firstly, a substrate 20 is provided, for example, an N-type or P-type silicon substrate 20 . Using a conventional CMOS image sensor process on an N-type or P-type silicon substrate 20, a photodiode 21, a transfer transistor 23, and a reset transistor 27 are formed, and a storage node is formed on the substrate 20 between the transfer transistor 23 and the reset transistor 27. 29 : Including the gate oxide, polycrystalline gate and sidewalls forming the conventional transfer transistor 23 and reset transistor 27 .

Next, as shown in FIG. 5 , a metal masking layer material 24' is deposited on the entire surface of the silicon substrate 20. The metal masking layer material 24' can be formed using conventional metal or metal compound materials in the CMOS process, including one or more of metal or metal compound materials such as titanium, titanium nitride, tungsten, aluminum, copper, cobalt, and nickel. , forming a single-layer structure or a multi-layer composite structure.

Metal masking layer material 24' may be deposited to a total thickness between 10 Angstroms and 10,000 Angstroms.

As shown in FIG. 6 again, photolithography and etching of the metal masking layer are performed to remove the metal masking layer material 24' above the photodiode 21, and at the same time form a metal masking layer opening 31 above the storage node 29, thereby forming a metal masking layer. The masking layer 24 is patterned.

Next, as shown in FIG. 7 , an insulating reflective layer material 28' is deposited on the entire surface of the silicon substrate 20, for example, a composite insulating reflective layer material 28' may be deposited on the entire silicon wafer substrate 20. The composite insulating reflection layer can be formed by stacking at least two materials among materials such as silicon nitride, silicon dioxide, silicon oxynitride, and nitrogen-containing silicon carbide. Moreover, the material or refractive index between any two adjacent layers in the formed composite insulating reflection layer is different. Incident light can be effectively reflected by stacking two or more insulating dielectric films with large differences in refractive index.

The opening 31 of the metal masking layer is filled with the deposited compound insulating reflective layer material 28'.

Subsequently, as shown in FIG. 8 , photolithography and etching are performed on the material 28' of the composite insulating reflective layer, and a pattern of the composite insulating reflective layer 28 is formed above the storage node 29. The size of the pattern of the composite insulating reflective layer 28 remaining after etching is greater than the size of the opening 31 of the metal masking layer, so as to completely seal the opening 31 of the metal masking layer.

Then as shown in FIG. 9, an interlayer dielectric 22 is deposited on the surface of the silicon substrate 20. For example, materials such as silicon dioxide and a low dielectric constant medium can be used as the interlayer dielectric 22, so that the transmission tube 23 and the reset tube 27 Device structures such as the compound insulating reflective layer 28 and the like are completely covered therein.

Subsequently, as shown in FIG. 10 , the photolithography and etching of the contact hole are carried out, and the composite insulating reflective layer material 28 ′ under the contact hole is removed by etching the contact hole, and the gap between the contact hole 25 and the metal masking layer 24 remains. The composite insulating reflection layer material 28 ′ forms a contact hole opening 25 ′ pattern passing through the insulating reflection layer 28 pattern and connecting to the storage node 29 .

Finally enter the conventional CMOS process, as shown in Figure 11, the filling of the contact hole is realized by deposition and chemical mechanical polishing. The contact hole 25 is formed after the hole opening 25' is filled with metal or metal compound.

It can be seen from FIG. 3 that the gap 30 that originally existed between the metal masking layer 24 and the contact hole 25 no longer exists due to the filling of the compound insulating reflective layer material 28' in the opening 31 of the metal masking layer.

As shown in FIG. 12, a metal interconnection material, such as metal copper, is deposited on the interlayer dielectric 22, and then through photolithography and etching, a subsequent metal interconnection layer 26 connecting the contact hole 25 is formed, thereby forming the metal interconnection layer 26 of FIG. Global pixel structure to reduce light leakage of storage nodes.

In summary, the present invention inserts an insulating reflective layer between the metal masking layer and the contact hole of the conventional global pixel unit, so that the light leakage gap between the metal masking layer and the contact hole is filled with the insulating reflective layer, and by using The stacking of more than two layers of insulating dielectric films of different materials or refractive indices forms a composite insulating reflective layer that reflects incident light, thus ensuring that incident light cannot enter the charge storage area of the storage node, reducing the global pixel unit storage capacity of the CMOS image sensor. At the same time, it ensures the electrical isolation between the metal masking layer and the contact hole, thereby effectively ensuring the accuracy of the signal in the storage capacitor of the global exposure pixel unit, avoiding the distortion of the output signal, and finally enabling the image sensor to obtain high quality images.

The above are only preferred embodiments of the present invention, and the embodiments are not intended to limit the scope of patent protection of the present invention. Therefore, all equivalent structural changes made by using the description and accompanying drawings of the present invention should be included in the scope of the present invention in the same way. within the scope of protection.

Claims (10)

1. a kind of global pixel structure reducing memory node light leakage, which is characterized in that include two pole of photoelectricity on substrate Pipe, transfer tube and reset transistor, and the memory node that is formed on the substrate between transfer tube and reset transistor；Wherein, institute It states on transfer tube, be covered with metal shadowing layer in reset transistor and on memory node, contact hole, institute are connected on the memory node It states contact hole across metal shadowing layer to be arranged, and forms gap between the metal shadowing layer, full of insulation in the gap Reflecting layer.

2. the global pixel structure according to claim 1 for reducing memory node light leakage, which is characterized in that the insulation is anti- It is the compound inslation reflection layer structure for stacking formation mutually by multilayer insulation medium to penetrate layer.

3. the global pixel structure according to claim 2 for reducing memory node light leakage, which is characterized in that described compound exhausted Refractive index in edge reflecting layer between two layers of dielectric of arbitrary neighborhood is different.

4. the global pixel structure according to claim 2 for reducing memory node light leakage, which is characterized in that described compound exhausted Material in edge reflecting layer between two layers of dielectric of arbitrary neighborhood is different.

5. the global pixel structure according to claim 1 for reducing memory node light leakage, which is characterized in that the metal is covered It is single layer structure or multi-layer compound structure to cover layer.

6. a kind of production method for the global pixel structure reducing memory node light leakage, which is characterized in that include the following steps：

One substrate is provided, forms photodiode, transfer tube and reset transistor over the substrate, and in transfer tube and reset transistor Between the substrate on form memory node；

Metal shadowing layer material is deposited in the substrate surface full sheet, and the metal shadowing layer material above photodiode is moved It removes, while metal shadowing layer opening is formed in the top of memory node, form metal shadowing layer；

Dielectric reflective layer material is deposited in the substrate surface full sheet, metal shadowing layer opening is full of, and on memory node It is rectangular at dielectric reflective layer pattern, so that insulative reflective layer dimension of picture is more than metal shadowing layer opening size；

Inter-level dielectric is deposited in the substrate surface full sheet, is formed in dielectric reflective layer pattern and connects connecing for memory node Contact hole figure；

The filling of contact hole is carried out, forms contact hole, and form the rear road metal interconnecting layer of connection contact hole.

7. the global pixel structure according to claim 6 for reducing memory node light leakage, which is characterized in that the substrate is In N-type or P-type silicon substrate.

8. the global pixel structure according to claim 6 for reducing memory node light leakage, which is characterized in that the metal is covered It is the single layer structure or multi-layer compound structure by one or more formation in titanium, titanium nitride, tungsten, aluminium, copper, cobalt and nickel to cover layer.

9. the global pixel structure according to claim 6 for reducing memory node light leakage, which is characterized in that the insulation is anti- Layer is penetrated to be by silicon nitride, silica, silicon oxynitride, stack the compound inslation formed reflection containing at least two in fire sand Layer structure.

10. the global pixel structure according to claim 9 for reducing memory node light leakage, which is characterized in that described compound Material or refractive index in insulative reflective layer between two layers of arbitrary neighborhood is different.