CN108847418A - A kind of image sensor structure and forming method enhancing near-infrared quantum efficiency - Google Patents
A kind of image sensor structure and forming method enhancing near-infrared quantum efficiency Download PDFInfo
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Abstract
The invention discloses a kind of image sensor structures for enhancing near-infrared quantum efficiency, including：Silicon substrate；Photodiode in the positive silicon substrate；Set on the positive transfer tube of the silicon substrate and light reflection structure；Wherein, the corresponding lower section for being located at photodiode of the light reflection structure；Interlayer dielectric layer set on silicon substrate front lower section, the metal interconnecting layer in interlayer dielectric layer；Wherein, the light reflection structure for will reflex in photodiode again from the light of silicon substrate back surface incident, to realize the collection to near-infrared incident ray, it ensure that near infrared light assimilation ratio in silicon substrate is substantially increased, to improve the near-infrared quantum efficiency of back-illuminated type pixel unit.The invention also discloses a kind of forming methods of image sensor structure for enhancing near-infrared quantum efficiency.
Description
Technical field
The present invention relates to image sensor technologies fields, can enhance near-infrared quantum efficiency more particularly, to one kind
Image sensor structure and forming method.
Background technique
Imaging sensor refers to the device for converting optical signals to electric signal, usually extensive commercial imaging sensor core
Piece includes charge-coupled device (CCD) and complementary metal oxide semiconductor (CMOS) image sensor chip two major classes.
Cmos image sensor is compared with traditional ccd sensor, has low-power consumption, inexpensive and compatible with CMOS technology
The features such as, therefore have been more and more widely used.Present cmos image sensor is applied not only to consumer electronics field, such as micro-
In type digital camera (DSC), mobile phone camera, video camera and digital single-lens reflex camera (DSLR), and in automotive electronics, monitoring, biology
The fields such as technology and medicine are also widely used.
The pixel unit of cmos image sensor is that imaging sensor realizes photosensitive core devices.Most common pixel list
Member is the active pixel structure comprising a photodiode and multiple transistors.Photodiode is photosensitive list in these devices
Member realizes collection and photoelectric conversion to light, and other MOS transistors are control units, main to realize to photodiode
Choose, reset, signal amplification and read control.
Cmos image sensor is different according to the path that incident light enters photodiode, can be divided into front-illuminated and back-illuminated
Two kinds of imaging sensors of formula, the imaging sensor front-illuminated for referring to incident light and entering photodiode from front side of silicon wafer, and back-illuminated
Formula refers to that incident light enters the imaging sensor of photodiode from silicon chip back side.
In order to improve the area of photodiode in cmos image sensor and reduce loss of the dielectric layer to incident light, I
Can use back-illuminated cmos image sensors technique, i.e., incident light enters photodiode from the back side of silicon wafer, to subtract
Loss of the small dielectric layer to incident light, improves the sensitivity of pixel unit.
Silicon materials reduce the absorption coefficient of incident light with the increase of wavelength.Conventional pixel cell usually using it is red, green,
The filter layer of primary colors.Wherein the wavelength of blue light is 450 nanometers, and the wavelength of green light is 550 nanometers, and the wavelength of feux rouges is 650
Nanometer.Therefore absorption position of the feux rouges in silicon wafer is most deep, and blue light is most shallow.Blue light is inhaled in the position near silicon chip surface
It receives, absorption coefficient highest；It is most deep that feux rouges enters silicon wafer, can about enter 2.3 microns of silicon wafer, absorption coefficient is most
It is low；Between the two between blue light and feux rouges, and the absorption of near infrared light needs the absorption greater than 2.3 microns to the absorption coefficient of green light
Thickness.
A kind of structure of conventional back-illuminated cmos image sensors pixel unit is as shown in Figure 1.Wherein, in silicon substrate 10
The photodiode 11 of middle formation is the sensor devices of pixel unit, and the visible light part in incident ray passes through photoelectric conversion shape
At charge be collected in the photodiode.Since 10 thickness of silicon substrate of back-illuminated type pixel unit is usually in 3 microns,
And the near-infrared part in incident light needs the Si-Substrate Thickness much larger than 3 microns that can just be absorbed.Therefore as shown in Figure 1, entering
Penetrating the near-infrared part in light (near-infrared incident ray) will be directly through silicon substrate 10, subsequently into inter-level dielectric 12.Due to
Inter-level dielectric 12 in semiconductor technology is using translucent materials such as silica, therefore near-infrared incident ray will be directly through silicon
Substrate 10 and inter-level dielectric 12, cannot achieve normal photoelectric conversion, therefore quantum efficiency is extremely low.
In the application of current safety monitoring, machine vision and intelligent transportation system, the light wave of night infrared light filling
Length concentrates on 850 nanometers to 940 nanometers, and conventional back-illuminated type pixel unit is insensitive to the light of this wave band.
Therefore, it is necessary to design new back-illuminated type pixel cell structure and forming method, to improve the sensitive of near infrared band
Degree, promotes the night vision effect of product.
Summary of the invention
It is an object of the invention to overcome drawbacks described above of the existing technology, a kind of enhancing near-infrared quantum efficiency is provided
Image sensor structure and forming method.
To achieve the above object, technical scheme is as follows：
The present invention provides a kind of image sensor structures for enhancing near-infrared quantum efficiency, including：
Silicon substrate；
Photodiode in the positive silicon substrate；
Set on the positive transfer tube of the silicon substrate and light reflection structure；Wherein, the light reflection structure is corresponding is located at light
The lower section of electric diode；
Interlayer dielectric layer set on silicon substrate front lower section, the metal interconnecting layer in interlayer dielectric layer；Wherein,
The light reflection structure for will reflex in photodiode again from the light of silicon substrate back surface incident, with reality
Now to the collection of near-infrared incident ray.
Further, the gate structure same layer that the light reflection structure and transfer tube are equipped with is arranged.
Further, the light reflection structure is to set the complex reflex layer formed by different materials are folded.
Further, the light reflection structure includes the metal positioned at the polysilicon layer on upper layer and positioned at polysilicon layer lower layer
Silicide layer.
Further, the polysilicon layer and metal silicide layer are drawn and are grounded by metal interconnecting layer.
Further, further include：Shallow-trench isolation in the silicon substrate and for photodiode to be isolated.
Further, further include：Metal light blocking layer on the silicon substrate back side and between pixel.
Further, further include：Anti-reflecting layer between the silicon substrate backside surface and metal light blocking layer.
The present invention also provides a kind of forming methods of image sensor structure for enhancing near-infrared quantum efficiency, including：
One silicon substrate is provided, forms photodiode and shallow-trench isolation in the positive silicon substrate；
Transfer tube and light reflection structure are formed in the front of the silicon substrate, and makes the light reflection structure is corresponding to be located at light
The top of electric diode；
In the front deposit interlayer dielectric layer of the silicon substrate, and metal interconnecting layer is formed in interlayer dielectric layer；
It will be adhered on slide glass after silicon substrate overturning, reduction process then executed to the back side of the silicon substrate；
Using back-illuminated technique, anti-reflecting layer is deposited in the backside surface of the silicon substrate, and formed on anti-reflecting layer
Metal light blocking layer.
Further, the forming method of the light reflection structure includes：
When forming transfer tube, in the front depositing polysilicon material of the silicon substrate, by being carried out to polycrystalline silicon material
Lithography and etching, it is rectangular in groups at the lowest polysilicon layer of light reflection structure on the photodiode, it is formed simultaneously pixel unit
The polysilicon gate of transfer tube；
In the front depositing silicide barrier material of the silicon substrate, by carrying out photoetching to silicide barrier layer material
And etching, and Metal deposition and silicidation reaction are carried out, only in the formation group on the polysilicon layer above photodiode
At the upper layer metal silicide layer of light reflection structure.
It can be seen from the above technical proposal that the present invention passes through under the photodiode of back-illuminated cmos image sensors
Side's setting light reflection structure, light reflection structure metal silicide and polysilicon can be used to form complex reflex layer, realize to close
The reflection and collection of infrared incident light ensure that near infrared light assimilation ratio in silicon substrate is substantially increased, to improve
The near-infrared quantum efficiency of back-illuminated type pixel unit.
Detailed description of the invention
Fig. 1 is a kind of structural schematic diagram of existing back-illuminated cmos image sensors pixel unit；
Fig. 2 is a kind of image sensor structure signal of enhancing near-infrared quantum efficiency of a preferred embodiment of the present invention
Figure；
Fig. 3-Figure 10 is a kind of shape of the imaging sensor of enhancing near-infrared quantum efficiency of a preferred embodiment of the present invention
At the processing step schematic diagram of method.
Specific embodiment
With reference to the accompanying drawing, specific embodiments of the present invention will be described in further detail.
It should be noted that in following specific embodiments, when describing embodiments of the invention in detail, in order to clear
Ground indicates structure of the invention in order to illustrate, spy does not draw to the structure in attached drawing according to general proportion, and has carried out part
Amplification, deformation and simplified processing, therefore, should be avoided in this, as limitation of the invention to understand.
In specific embodiment of the invention below, referring to Fig. 2, Fig. 2 is one kind of a preferred embodiment of the present invention
Enhance the image sensor structure schematic diagram of near-infrared quantum efficiency.As shown in Fig. 2, a kind of enhancing near-infrared quantum of the invention
The image sensor structure of efficiency is established on silicon substrate 20.Wherein, in the front of silicon substrate 20, and it is located in silicon substrate 20
It is provided with photodiode 21, the shallow-trench isolation 22 of cmos image sensor pixel unit；It is also set on the front of silicon substrate 20
There are each MOS transistor, such as transfer tube 24 and the suspending drain 23 of pixel unit etc.；In the front face surface of silicon substrate 20
It is additionally provided with interlayer dielectric layer 33, metal interconnecting layer 30 and 32 is provided in interlayer dielectric layer 33.To use double layer of metal to interconnect
For the pixel unit of layer 30 and 32, carried out mutually between the metal interconnecting layer 30 and 32 of each layer by contact hole 29 and through-hole 31
Even.
Wherein, photodiode 21 is photosensitive unit, realizes the collection to light and is responsible for photoelectric conversion, photon is converted
For electronics；Other MOS transistors are control units, it is main realize to the choosing of photodiode 21, reset, signal amplification and
The control of reading, it may include such as transfer tube 24, reset transistor, source electrode follow pipe and line EAC；Wherein transfer tube 24 is responsible will
The electron-transport generated in photodiode 21 is converted to voltage signal output to suspending drain 23.Shallow-trench isolation 22 is used for
Photodiode 21 is isolated, i.e., for pixel to be isolated.
Please refer to Fig. 2.In the front of silicon substrate 20, and it is located at the corresponding lower section of each photodiode 21, also sets respectively
It is equipped with light reflection structure 27 and 28.Light reflection structure 27 and 28 from the light of 20 back surface incident of silicon substrate for will reflex to again
In photodiode 21, to realize the collection to near-infrared incident ray.
Transfer tube 24 is equipped with gate structure in the front face surface of silicon substrate 20；Light reflection structure 27 and 28 can be with transfer tube
24 gate structure same layer setting.
Light reflection structure 27 and 28 can be carried out folding by different materials and be set, so that being formed, there is the light of complex reflex layer to reflect knot
Structure 27 and 28.For example, the grid of transfer tube 24 is usually polysilicon gate, then light reflection structure 27 and 28 may include being located at upper layer
Polysilicon layer 27 and metal silicide layer 28 positioned at 27 lower layer of polysilicon layer, form complex reflex layer 27 and 28.In this way, can
While using the polysilicon gate for forming transfer tube 24, the light reflection structure 27 and 28 containing polysilicon layer 27 is formed.
The absorbability of incident light is directly related to the thickness of silicon substrate collecting zone, and near infrared light due to wavelength compared with
Long, the depth absorbed is much larger than conventional bluish-green red trichromatism.In order to enhance pixel unit to the absorbability of near infrared light, need
Photoelectric conversion will be realized after the near-infrared the reflection of generation incident light light echo electric diode 21 of break-through silicon substrate 20.
Due to being the inter-level dielectric 33 of light transmission below Conventional photodiode 21, the reflection to incident light cannot achieve；Cause
This, the present invention increases metal silicide layer 28 below photodiode 21 to reflect incident light.And due to pixel
The dark current and white pixel performance and metal contamination of unit are directly related, if directly forming metal silicide on a silicon substrate
As reflecting layer, the performance of pixel unit can be adversely affected.It is thus impossible to which metal silicide layer 28 is directly formed
On silicon substrate 20 below photodiode 21.
The present invention is using the metal silicide on the polysilicon in common process, to realize to the anti-of near-infrared incident light
It penetrates.Although polysilicon is light transmission, the metal silicide for being located at (referring to relative position when production) above polysilicon is not
Light transmission, to realize the reflection to near-infrared incident light while avoiding metal contamination.
Polysilicon layer 27 and metal silicide layer in order to realize the abundant reflection to near-infrared incident ray, for reflection
28 area will sufficiently cover photodiode 21, to guarantee that the near-infrared incident light of reach throught photodiode 21 can not worn
Saturating gap.
The present invention is formed by 28 structure of polysilicon layer 27 and metal silicide layer formed below photodiode 21
After entering photodiode 21 photovoltaic reaction occurs for the reflection to near-infrared incident ray, reflection light, reacts the charge of generation
It is collected by the Built-in potential of photodiode 21, forms electric signal and improved to realize the collection of near-infrared incident ray
The quantum efficiency of pixel unit near-infrared.
Simultaneously as polysilicon layer 27 and metal silicide layer 28 are formed in 21 lower section of photodiode, polysilicon layer 27
On current potential will have a direct impact on the Built-in potential of photodiode 21, therefore, it is necessary to by polysilicon layer 27 and metal silicide
Layer 28 is by such as contact hole 29 and the extraction of first layer metal interconnection layer 30 in metal interconnecting layer 30 and 32 and is grounded, to avoid
The influence that photodiode 21 is worked normally.
In addition, the also settable metal light blocking layer 25 on the back side of silicon substrate 20 and between pixel；Each metal gear
Photo structure forms opening in the top of corresponding photodiode 21, to guide light to enter from the opening and to expose to photoelectricity two
Pole pipe 21.
As needed, the also settable anti-reflecting layer 26 between the backside surface of silicon substrate 20 and metal light blocking layer 25.
Below by specific embodiment and attached drawing, to a kind of image sensing of enhancing near-infrared quantum efficiency of the invention
The forming method of device structure is described in detail.
Fig. 3-Figure 10 is please referred to, Fig. 3-Figure 10 is a kind of enhancing near-infrared quantum efficiency of a preferred embodiment of the present invention
The processing step schematic diagram of the forming method of imaging sensor.As shown in Fig. 3-Figure 10, a kind of enhancing near-infrared amount of the invention
The forming method of the image sensor structure of sub- efficiency can be used to form the image sensing of above-mentioned enhancing near-infrared quantum efficiency
Device structure, and may include following steps：
For using the pixel unit of double layer of metal interconnection layer, firstly, as shown in figure 3, one silicon substrate 20 of offer, uses
Conventional cmos image sensor process process forms photodiode 21 in positive silicon substrate 20 (front of silicon substrate 20)
With shallow-trench isolation 22.
Then, as shown in figure 4, by polycrystalline silicon material deposit, lithography and etching, transmission is formed in the front of silicon substrate 20
Pipe 24 and light reflection structure 27 and 28.Specifically may include：It is initially formed the polysilicon gate 24 ' of pixel unit transfer tube 24, simultaneously
20 front of silicon substrate above photodiode 21 is correspondingly formed the lowest polysilicon layer 27 of composition light reflection structure 27 and 28.
Then, as shown in figure 5, using photoetching and ion implanting in the front of silicon substrate 20, the suspension of pixel unit is formed
Drain electrode 23.Form complete transfer tube 24.
Then as shown in fig. 6, silicon substrate 20 front depositing silicide barrier material, by silicide barrier layer
Material carries out lithography and etching, and carries out Metal deposition and silicidation reaction, only more above photodiode 21
The upper layer metal silicide layer 28 of composition light reflection structure 27 and 28 is formed on crystal silicon layer 27.Form complete light reflection structure 27
With 28.
Then as shown in fig. 7, being deposited in the front face surface of silicon substrate 20 by using conventional cmos metal interconnection process
Inter-level dielectric layer material forms interlayer dielectric layer 33；It is formed in double layer of metal interconnection layer 30 and 32 in interlayer dielectric layer 33
First layer metal interconnection layer 30, and on the lowest polysilicon layer of light reflection structure 27 and 28 27 and upper layer metal silicide layer 28
Form the contact hole 29 of connection first layer metal interconnection layer 30.
Then as shown in figure 8, using conventional cmos metal interconnection process, through-hole 31 and second layer metal interconnection are continuously formed
Layer 32.
Then as shown in figure 9, being adhered on slide glass 34 after silicon substrate 20 is overturn, then the back side of silicon substrate 20 is executed
Reduction process.The thickness of silicon substrate 20 can be in 3 microns after being thinned.
It is last as shown in Figure 10, using back-illuminated technique, anti-reflecting layer material is deposited in the backside surface of silicon substrate 20, is formed
Anti-reflecting layer 26, and by the technical process such as the deposit and photoetching of the metal materials such as aluminium, tungsten and copper, etching, in anti-reflecting layer
The graphic structure of metal light blocking layer 25 is formed on 26.
In conclusion the present invention reflects knot by the way that light is arranged below the photodiode of back-illuminated cmos image sensors
Structure, light reflection structure metal silicide and polysilicon can be used to form complex reflex layer, realize to the anti-of near-infrared incident light
It penetrates and collects, ensure that near infrared light assimilation ratio in silicon substrate is substantially increased, to improve back-illuminated type pixel unit
Near-infrared quantum efficiency.
Above is merely a preferred embodiment of the present invention, the scope of patent protection that embodiment is not intended to limit the invention,
Therefore all to change with equivalent structure made by specification and accompanying drawing content of the invention, it similarly should be included in of the invention
In protection scope.
Claims (10)
1. a kind of image sensor structure for enhancing near-infrared quantum efficiency, which is characterized in that including：
Silicon substrate；
Photodiode in the positive silicon substrate；
Set on the positive transfer tube of the silicon substrate and light reflection structure；Wherein, the light reflection structure is corresponding is located at photoelectricity two
The lower section of pole pipe；
Interlayer dielectric layer set on silicon substrate front lower section, the metal interconnecting layer in interlayer dielectric layer；Wherein,
The light reflection structure for will reflex in photodiode again from the light of silicon substrate back surface incident, with realization pair
The collection of near-infrared incident ray.
2. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 1, which is characterized in that the light
The gate structure same layer that catoptric arrangement and transfer tube are equipped with is arranged.
3. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 1, which is characterized in that the light
Catoptric arrangement is to set the complex reflex layer formed by different materials are folded.
4. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 1, which is characterized in that the light
Catoptric arrangement includes the metal silicide layer positioned at the polysilicon layer on upper layer and positioned at polysilicon layer lower layer.
5. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 4, which is characterized in that described more
Crystal silicon layer and metal silicide layer are drawn and are grounded by metal interconnecting layer.
6. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 1, which is characterized in that also wrap
It includes：Shallow-trench isolation in the silicon substrate and for photodiode to be isolated.
7. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 1, which is characterized in that also wrap
It includes：Metal light blocking layer on the silicon substrate back side and between pixel.
8. the image sensor structure of enhancing near-infrared quantum efficiency according to claim 7, which is characterized in that also wrap
It includes：Anti-reflecting layer between the silicon substrate backside surface and metal light blocking layer.
9. a kind of forming method for the image sensor structure for enhancing near-infrared quantum efficiency, which is characterized in that including：
One silicon substrate is provided, forms photodiode and shallow-trench isolation in the positive silicon substrate；
Transfer tube and light reflection structure are formed in the front of the silicon substrate, and makes the light reflection structure is corresponding to be located at photoelectricity two
The top of pole pipe；
In the front deposit interlayer dielectric layer of the silicon substrate, and metal interconnecting layer is formed in interlayer dielectric layer；
It will be adhered on slide glass after silicon substrate overturning, reduction process then executed to the back side of the silicon substrate；
Using back-illuminated technique, anti-reflecting layer is deposited in the backside surface of the silicon substrate, and metal is formed on anti-reflecting layer
Light blocking layer.
10. the forming method of the image sensor structure of enhancing near-infrared quantum efficiency according to claim 9, feature
It is, the forming method of the light reflection structure includes：
When forming transfer tube, in the front depositing polysilicon material of the silicon substrate, by carrying out photoetching to polycrystalline silicon material
And etching, it is rectangular in groups at the lowest polysilicon layer of light reflection structure on the photodiode, it is formed simultaneously pixel unit transmission
The polysilicon gate of pipe；
In the front depositing silicide barrier material of the silicon substrate, by carrying out photoetching and quarter to silicide barrier layer material
Erosion, and Metal deposition and silicidation reaction are carried out, composition light is only formed on the polysilicon layer being located above photodiode
The upper layer metal silicide layer of catoptric arrangement.
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