CN102231384B - Image sensor and manufacturing method thereof - Google Patents

Abstract

An image sensor and its forming method, wherein the image sensor includes: a semiconductor substrate, a pixel array is formed in the semiconductor substrate, the pixels include photosensitive units, and adjacent pixels are separated by shallow trench insulation structures; A light-transmitting layer on the surface of the semiconductor substrate, the light-transmitting layer is aligned with the photosensitive unit; an opaque layer on the surface of the semiconductor substrate, the opaque layer surrounds the light-transmitting layer; located in the opaque layer The metal layer and the conductive plug connecting the adjacent metal layer. The image sensor pixel can effectively prevent incident light from entering other photosensitive units, avoid optical crosstalk, and improve the image display quality of the image sensor pixel.

Description

Image sensor and method of forming the same

technical field

The invention relates to the field of CMOS image processing, in particular to an image sensor and a forming method thereof.

Background technique

Currently, image sensors are widely used in cameras, medical equipment, cellular phones, automobiles, and other occasions. The manufacturing process of image sensors, especially the CMOS (Complementary Metal Oxide Semiconductor) image sensor (CIS), has made great progress, and has continuously promoted the development of image sensors in the direction of high integration and miniaturization. Each pixel of an image sensor typically includes a light-sensing element, such as a photodiode, and one or more transistors for reading out signals from the light-sensing element. CMOS image sensors use metal wires to connect each photosensitive unit with other photosensitive units and output terminals; these metal wires are generally distributed in different layers to connect with different parts of the transistor and form an effective path.

The Chinese patent application with application number 200710148796.5 discloses an image sensor as shown in FIG. 1. Referring to FIG. A photosensitive unit forms a photosensitive unit array, a dielectric layer 102 positioned on the surface of the photosensitive unit 101 and a metal layer 103 positioned in the dielectric layer, a first flat layer 104 positioned on the surface of the dielectric layer 102, and a color filter positioned on the surface of the first flat layer 104 sheet 105 , the second flat layer 106 on the surface of the color filter 105 , and the microlens 107 on the surface of the second flat layer 106 .

Existing image sensors include backside illuminated image sensor (BSI image sensor) and front illuminated image sensor (FSI image sensor). Both backside-illuminated and front-side-illuminated image sensors typically suffer from an important problem: optical crosstalk.

As shown in FIG. 2 , in the image sensor, when the incident light 290 irradiates the photosensitive unit 101 at a certain inclination angle, a part of the light enters the photosensitive unit 101 through a transparent interlayer dielectric layer (not shown), and a part of the light irradiates the metal layer 1032 , 1033; since some of the metal layers 1031, 1032, 1033 do not need conductive plug connections, but are filled with transparent interlayer dielectric layers, this part of the light irradiated on the metal layers 1032, 1033 is reflected and finally enters the In other photosensitive units 101 (generally adjacent photosensitive units), optical crosstalk is formed. This optical crosstalk creates artifact components in the image that cannot be corrected in image processing, seriously affecting image quality.

Contents of the invention

The problem to be solved by the present invention is to provide an image sensor and its forming method, so as to solve the problem of optical crosstalk caused by incident light reflected by a metal layer and entering adjacent photosensitive units in the existing image sensor.

In order to solve the above problems, the present invention adopts the following technical solutions:

An image sensor, comprising: a semiconductor substrate, a pixel array is formed in the semiconductor substrate, the pixels include photosensitive units, and adjacent pixels are separated by shallow trench insulation structures; The light layer, the light-transmitting layer is aligned with the photosensitive unit; the light-proof layer located on the surface of the semiconductor substrate, the light-proof layer surrounds the light-transmitting layer; the metal layer located in the light-proof layer and connected adjacent Conductive plugs for the metal layer.

Optionally, the material of the opaque layer is an insulating material.

Optionally, the insulating material is a silicon oxynitride compound.

Optionally, the material of the metal layer and the conductive plug is doped polysilicon, aluminum, copper or tungsten.

Optionally, it further includes: a passivation layer covering the uppermost metal layer, and a plurality of microlenses on the passivation layer corresponding to the photosensitive units one by one.

A method for forming an image sensor, comprising the following steps: providing a semiconductor substrate, a pixel array is formed in the semiconductor substrate, the pixels include photosensitive units, and adjacent pixels are separated by shallow trench insulation structures; An etch stop layer is formed on the semiconductor substrate; a first opaque layer is formed on the etch stop layer, and the opaque layer covers the photosensitive unit and the shallow trench isolation structure; forming a first through hole in the transparent layer; filling the first through hole with a conductive substance to form a first conductive plug; forming a discrete first metal layer on or in the first opaque layer, the The first metal layer communicates with the first conductive plug; a second light-proof layer covering the first metal layer is formed on the first light-proof layer; a second conductive plug is formed in the second light-proof layer; A discrete second metal layer is formed on or in the second opaque layer, and the second metal layer communicates with the second conductive plug; continue to form a predetermined number of opaque layers, metal layers, and penetrating through the thickness of the opaque layer A conductive plug connected to the metal layer; a passivation layer covering the last metal layer is formed on the last opaque layer; the passivation layer and the opaque layer are etched to expose the etching stop layer, forming a vertical pair The groove of the quasi-photosensitive unit; the groove is filled with a light-transmitting material to form a light-transmitting layer.

Optionally, the material of the opaque layer is an insulating material.

Optionally, the etching stop layer material is a light-transmitting material.

Optionally, the insulating material is a silicon oxynitride compound.

Compared with the prior art, the present invention has the following advantages:

The image sensor provided by the embodiment of the present invention includes a light-transmitting layer on the surface of the semiconductor substrate, the light-transmitting layer is aligned with the photosensitive unit; an opaque layer on the surface of the semiconductor substrate, the light-opaque layer surrounds Light-transmitting layer; the metal layer located in the light-impermeable layer and the conductive plug connecting the adjacent metal layer; when the incident light hits the image sensor pixel, the incident light will only enter the corresponding photosensitive unit through the light-transmitting layer, and cannot pass through The opaque layer around the light-transmitting layer enters other photosensitive units, avoiding optical crosstalk to other photosensitive units.

Furthermore, in the method for forming an image sensor provided by the embodiment of the present invention, a transparent layer is provided at the position aligned with the photosensitive unit, and an opaque layer is provided around the transparent layer, so that incident light can only enter the corresponding sensor through the transparent layer. The photosensitive unit cannot enter other photosensitive units, which avoids the formation of optical crosstalk to other photosensitive units.

Description of drawings

FIG. 1 is a schematic structural diagram of an existing image sensor;

FIG. 2 is a schematic diagram of optical crosstalk formed by an existing image sensor;

Fig. 3 is a schematic diagram of a specific embodiment of an image sensor of the present invention;

Fig. 4 is a schematic diagram of preventing optical crosstalk of the image sensor of the present invention;

5 is a schematic flow chart of a specific embodiment of the image sensor forming method of the present invention;

6 to 15 are schematic diagrams of specific embodiments of the image sensor forming method of the present invention.

Detailed ways

The inventors of the present invention found that in the existing image sensor, when the incident light is incident at a certain inclination angle, part of it reaches the photosensitive unit through the transparent interlayer dielectric layer, and the other part is irradiated on the metal layer and reflected. Since the position between the metal layers not connected by the conductive plug is filled with a transparent interlayer dielectric layer, the incident light irradiated at this position is reflected multiple times by the metal layer, and finally enters other photosensitive units (generally adjacent photosensitive cells) unit), forming optical crosstalk, which seriously affects the image display quality of the image sensor.

In view of the above problems, the inventor proposed an image sensor after research and analysis, including: a semiconductor substrate, a pixel array is formed in the semiconductor substrate, the pixels include photosensitive units, and shallow trenches are used to insulate adjacent pixels. The structure is separated; the light-transmitting layer on the surface of the semiconductor substrate, the light-transmitting layer is aligned with the photosensitive unit; the light-proof layer on the surface of the semiconductor substrate, the light-proof layer surrounds the light-transmitting layer; The metal layer in the transparent layer and the conductive plug connecting adjacent metal layers.

In the image sensor provided by the present invention, since the light-transmitting layer is only arranged above the photosensitive unit, and the surrounding of the light-transmitting layer is an opaque layer, when the incident light enters the image sensor pixel, the incident light will only travel along the The light layer enters the corresponding photosensitive unit, but cannot enter the adjacent photosensitive unit through the opaque layer located around the transparent layer, thereby avoiding optical crosstalk to adjacent photosensitive units and improving the image display quality of the image sensor pixels.

The image sensor provided by the present invention will be further described below with reference to the drawings and embodiments.

FIG. 3 is a schematic structural diagram of a specific embodiment of the image sensor of the present invention. As shown in Figure 3, the image sensor of the present invention includes:

A semiconductor substrate 200, an array of pixels is formed in the semiconductor substrate 200, and the pixels include a photosensitive unit 202, and adjacent pixels are separated by a shallow trench insulation structure 201; a light-transmitting layer located on the surface of the semiconductor substrate 200 250, the light-transmitting layer 250 is aligned with the photosensitive unit 202; the opaque layer 210 located on the surface of the semiconductor substrate 200, the opaque layer 210 surrounding the light-transmitting layer 250; The metal layer 220 and the conductive plug 230 connected to the adjacent metal layer.

In this embodiment, the semiconductor substrate 200 can be a silicon-on-insulator substrate (SOI substrate), a quartz substrate, a ceramic substrate, a glass substrate, and there are other devices for image sensors on the substrate (Fig. not shown). The pixel includes a photosensitive unit 202, and the photosensitive unit 202 includes a plurality of photosensitive elements, such as photodiodes and color light sensors. The adjacent pixels are separated by shallow trench isolation structures 201 .

The transparent layer 250 is located directly above the photosensitive unit 202 , and the material of the transparent layer 250 is a transparent material, such as silicon oxide, so that light enters the photosensitive unit 202 after entering the transparent layer from the outside.

The opaque layer 210 is located around the opaque layer 250 and is formed of an opaque insulating material, such as silicon oxynitride compound. Light cannot pass through the opaque layer 210, so light will not be generated between adjacent pixels. Optical crosstalk; the opaque layer 210 is a multi-layer structure.

The metal layer 220 is located in the opaque layer 210; the metal layer 220 can be a multilayer structure, and in an example of the present invention, the metal layer 220 is a 3-layer structure; the metal layer 220 can be Electrically connected to an external light detection component (not shown), each metal layer 220 has a certain layout and will not block the photosensitive unit 202 . The place where electrical connection is required between the different metal layers 220 is connected by a conductive plug 230; the material of the metal layer 220 and the conductive plug 230 can be any conductive metal, such as doped polysilicon, aluminum, copper or tungsten; in one example of the invention, the material of choice is aluminum metal.

In this embodiment, the image sensor further includes a passivation layer 240 covering the uppermost metal layer 220, a color filter 260 located on the passivation layer 240 and the light-transmitting layer 250, located on the color filter A flat layer 270 on the flat layer 260 , and a plurality of microlenses 280 on the flat layer 270 corresponding to the photosensitive units 202 one-to-one.

The material of the passivation layer 240 is consistent with that of the transparent layer 250 .

The color filter 260 can be a color filter provided by the prior art. In an example of this embodiment, the material used to form the color filter 260 is dyed photoresist. A filter is formed at a position facing each photosensitive unit 202 , and each filter passes light of a different color, such as red, green and blue.

The material of the flat layer 270 is an organic material.

The surface of the microlens 280 facing the flat layer is flat, and the surface facing away from the flat layer is convex, and each microlens is aligned with the center of the corresponding photosensitive unit 202 . The material used to form the microlens 280 can be oxide or organic. The refractive index of the material used to form the microlens is between 1.4 and 1.6. Preferably, there is an organic thin film with a low refractive index on the surface of the microlens 280, so that the reflection is weakened, thereby increasing the light transmittance. The refractive index of the low refractive index material is between 1.1 and 1.4.

In this embodiment, according to actual design requirements, a flat layer may be added between the passivation layer 240 and the color filter 260, or the entire structure may not use a flat layer, but this change does not affect the essence of the present invention.

In this embodiment, if the image sensor pixels are only used in the black color field, the color filter 260 may not be provided.

FIG. 4 is a schematic diagram of preventing optical crosstalk according to a specific embodiment of the image sensor of the present invention. As shown in FIG. 4 , when the incident light 290 irradiates the image sensor pixel at a certain oblique angle, the incident light 290 can only enter the photosensitive unit 202 through the transparent layer 250 . This is because the light-transmitting layer 250 is only arranged on the top of the photosensitive unit 202, and the surrounding of the light-transmitting layer 250 is the opaque layer 210, so when the incident light 290 enters the sidewall of the light-transmitting layer 250, it will be received by The blocking of the opaque layer 210 around the optical layer 250 makes it impossible to enter the adjacent photosensitive unit 202, avoiding optical crosstalk to adjacent photosensitive units, improving the image display quality of the image sensor pixels, thereby avoiding optical crosstalk and improving The image display quality of the image sensor.

In addition, the invention also provides a method for forming an image sensor. FIG. 5 is a flow chart of a specific embodiment of the image sensor forming method of the present invention, specifically: as shown in FIG. 5 ,

Executing step S11, providing a semiconductor substrate, a pixel array is formed in the semiconductor substrate, the pixels include photosensitive units, and adjacent pixels are separated by shallow trench insulation structures;

Execute step S12, forming an etching stop layer on the semiconductor substrate;

Execute step S13, forming a first opaque layer on the etching stop layer, the opaque layer covering the photosensitive unit and the shallow trench isolation structure;

Execute step S14, forming a first through hole in the first opaque layer;

Executing step S15, filling the first through hole with a conductive substance to form a first conductive plug; performing step S16, forming a discrete first metal layer on or in the first opaque layer, the first The metal layer communicates with the first conductive plug;

Execute step S17, forming a second opaque layer covering the first metal layer on the first opaque layer;

Execute step S18, forming a second conductive plug in the second opaque layer;

Execute step S19, forming a discrete second metal layer on or in the second opaque layer, and the second metal layer communicates with the second conductive plug;

Execute step S20, continue to form a predetermined number of opaque layers, metal layers, and conductive plugs that penetrate through the thickness of the opaque layer and communicate with the metal layer;

Execute step S21, forming a passivation layer covering the last metal layer on the last opaque layer;

Executing step S22, etching the passivation layer and the opaque layer to expose the etching stop layer, forming a groove vertically aligned with the photosensitive unit;

Step S23 is executed to fill the trench with a light-transmitting material to form a light-transmitting layer.

In the forming method of the image sensor provided by the embodiment of the present invention, a transparent layer is arranged above the alignment photosensitive unit, and an opaque layer is arranged around the transparent layer, so that the incident light only enters the corresponding photosensitive unit through the transparent layer, It cannot enter other photosensitive units, avoiding the formation of optical crosstalk to other photosensitive units, and effectively improving the image display quality of the graphics sensor pixels.

6 to 15 are schematic diagrams of specific embodiments of the image sensor forming method of the present invention. As shown in FIG. 6 , a semiconductor substrate 300 is provided; pixels are formed in the semiconductor substrate 300 , and the pixels include photosensitive units 302 ; adjacent pixels are separated by shallow trench isolation structures 301 .

In this embodiment, the material of the semiconductor substrate 300 is any material that can support the formation of the photosensitive unit 302, such as a silicon-on-insulator substrate (SOI substrate), a quartz substrate, a ceramic substrate, a glass substrate, and the substrate Other devices (not shown) for the image sensor are also formed on the bottom.

The photosensitive unit 302 includes a plurality of photosensitive elements, such as color light sensors and photodiodes.

As shown in FIG. 7 , an etching stop layer 310 is formed on the semiconductor substrate 300 .

In this embodiment, the material of the etching stop layer 310 is a transparent insulating material, such as silicon oxide, which is used to protect the semiconductor substrate 300 during etching.

As shown in FIG. 8 , a first opaque layer 320 is formed on the etching stop layer 310 .

In this embodiment, the material of the first opaque layer 320 is an opaque insulating material, such as silicon nitride oxide.

As shown in FIG. 9 , a first conductive plug 340 is formed in the first opaque layer 320 . The specific forming process is as follows: a first photoresist layer (not shown) is formed on the first opaque layer 320, and a through-hole pattern is defined; Pattern etching the first opaque layer 320 and the etching stop layer 310 to expose the semiconductor substrate 300 to form a first through hole; fill the through hole with conductive material, and use chemical mechanical polishing to flatten the conductive material until exposed The first opaque layer 320 forms a conductive plug 340 .

In this embodiment, the material of the conductive plug 340 is a common conductive substance, such as doped polysilicon, aluminum, copper or tungsten.

As shown in FIG. 10 , a discrete first metal layer 350 is formed on the first opaque layer 320 , and the metal layer 350 communicates with the first conductive plug 340 . The specific process of forming the first metal layer 350 is as follows: a metal layer is formed on the first opaque layer 320 by vacuum evaporation; a second photoresist layer (not shown) is formed on the metal layer, and the first metal layer is defined. A metal wiring pattern; using the second photoresist layer as a mask, etch the metal layer along the first metal wiring pattern by dry etching to expose the first opaque layer 320, forming the first metal layer 350; removing second photoresist layer.

As shown in FIG. 11 , continue to form the second metal layer 352 , the third metal layer 354 , the second opaque layer 322 , the third opaque layer 324 , the second conductive plug 342 , and the third conductive plug 344 . The specific process of forming each film layer is as described above for forming the first opaque layer 320 , the first conductive plug 340 , and the first metal layer 350 .

In this embodiment, only the formation to the third metal layer 354 is listed. If the number of metal layers is expected to be relatively large, the corresponding metal layers, opaque layers and conductive plugs can be formed according to the above method.

As shown in FIG. 12 , a passivation layer 360 covering the third metal layer 354 is formed on the third opaque layer 324 by chemical vapor deposition, and the passivation layer 360 is planarized.

In this embodiment, the material of the passivation layer 360 can be an organic material or an inorganic material, such as transparent silicon oxide, silicon nitride, which mainly protects components from moisture and scratches

As shown in FIG. 13 , the passivation layer 360 and the opaque layer are etched to expose the etching stop layer 310 to form a groove aligned with the photosensitive unit 302 . The specific formation process is as follows: a third photoresist layer (not shown) is formed on the passivation layer 360, and a groove pattern aligned with the photosensitive unit 302 is defined; using the third photoresist layer as a mask, Along the trench pattern, etch the passivation layer 360 and the third opaque layer 324 , the second opaque layer 322 and the first opaque layer 320 to expose the etching stop layer 310 to form trenches.

As shown in FIG. 14 , the groove is filled with a light-transmitting material to form a light-transmitting layer 370 .

In this embodiment, the light-transmitting material is silicon oxide light-transmitting insulating material.

In this embodiment, after the last metal layer 354 is formed, an opaque layer covering the last metal layer 354 can be formed, and then the passivation layer 360 can be formed. In this embodiment, after forming the last metal layer 354 and before forming the passivation layer 360, grooves may be formed and filled with a light-transmitting material to form a light-transmitting layer 370, and the light-transmitting layer 370 covers the last metal layer 354 ; and then form a passivation layer 360 on the transparent layer 370 .

As shown in FIG. 15 , a color filter 380 is formed on the surface of the light-transmitting layer 370, a flat layer 385 is formed on the surface of the color filter 380, and a plurality of photosensitive units are formed on the surface of the flat layer 385. microlens 390.

In this embodiment, the color filter 380 can be selected from the color filter provided by the prior art; a filter is formed at a position opposite to each photosensitive unit 302, and each filter passes through different colors of light such as red, green, and blue.

In this embodiment, the surface of the microlens 390 facing the flat layer is flat, and the surface facing away from the flat layer is convex, and each microlens 390 is aligned with the center of the corresponding photosensitive unit. The material used to form the microlens 390 can be oxide or organic. The refractive index of the material used to form the microlens 390 is between 1.4˜1.6. Preferably, there is an organic thin film with a low refractive index on the surface of the microlens 390, so that the reflection is weakened, thereby increasing the light transmittance. The refractive index of the low refractive index material is between 1.1 and 1.4.

In this embodiment, according to actual conditions, the flat layer 385 may not be provided. If the image sensor pixels are black and white image sensor pixels, no color filter 380 needs to be provided.

In the forming method of the image sensor provided by the embodiment of the present invention, a transparent layer is arranged above the alignment photosensitive unit, and an opaque layer is arranged around the transparent layer, so that the incident light only enters the corresponding photosensitive unit through the transparent layer, It cannot enter other photosensitive units, avoiding the formation of optical crosstalk to other photosensitive units, and effectively improving the image display quality of the graphics sensor pixels.

Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection should be based on the scope defined by the claims of the present invention.

Claims (7)

1. an imageing sensor is characterized in that, comprising:

Semiconductor substrate is formed with pel array in the described Semiconductor substrate, and described pixel packets contains photosensitive unit, separates with insulation structure of shallow groove between the neighbor;

Be positioned at the photic zone of semiconductor substrate surface, described photic zone is aimed at photosensitive unit;

Be positioned at the light non-transmittable layers of semiconductor substrate surface, described light non-transmittable layers is surrounded described photic zone, and described light non-transmittable layers is the silica nitrogen compound;

Be positioned at the metal level of light non-transmittable layers and the conductive plunger of connection adjacent metal.

2. imageing sensor according to claim 1 is characterized in that, polysilicon, aluminium, copper or the tungsten of the material of described metal level and conductive plunger for mixing.

3. imageing sensor according to claim 1 is characterized in that, also comprises: cover the passivation layer of topmost metal layer, be positioned at a plurality of and photosensitive unit lenticule one to one on the described passivation layer.

4. the formation method of an imageing sensor is characterized in that, may further comprise the steps:

Semiconductor substrate is provided, is formed with pel array in the described Semiconductor substrate, described pixel packets contains photosensitive unit, separates with insulation structure of shallow groove between the neighbor;

Form etching stop layer in described Semiconductor substrate;

Form the first light non-transmittable layers at described etching stop layer, described the first light non-transmittable layers covers described photosensitive unit and insulation structure of shallow groove;

In the first light non-transmittable layers, form the first through hole;

In described the first through hole, fill full conductive materials, form the first conductive plunger;

On the first light non-transmittable layers or the discrete the first metal layer of interior formation, described the first metal layer is communicated with the first conductive plunger;

Form the second light non-transmittable layers that covers the first metal layer in the first light non-transmittable layers;

In the second light non-transmittable layers, form the second conductive plunger;

On the second light non-transmittable layers or the second discrete metal level of interior formation, described the second metal level is communicated with the second conductive plunger;

Continue to form light non-transmittable layers, the metal level of predetermined quantity and run through the conductive plunger that light non-transmittable layers thickness is communicated with metal level;

In the end form the passivation layer that covers last one deck metal level on one deck light non-transmittable layers;

Etching passivation layer and light non-transmittable layers form the groove of perpendicular alignmnet photosensitive unit to exposing etching stop layer;

In groove, fill full light transmissive material, form photic zone.

5. formation method according to claim 4 is characterized in that, described light non-transmittable layers material is insulating material.

6. formation method according to claim 4 is characterized in that, described etching stopping layer material is light transmissive material.

7. formation method according to claim 5 is characterized in that, described insulating material is the silica nitrogen compound.

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