CN102856337A - Pixel unit, CMOS (complementary metal oxide semiconductor) image sensor and manufacturing method of pixel unit - Google Patents
Pixel unit, CMOS (complementary metal oxide semiconductor) image sensor and manufacturing method of pixel unit Download PDFInfo
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- CN102856337A CN102856337A CN2012103042257A CN201210304225A CN102856337A CN 102856337 A CN102856337 A CN 102856337A CN 2012103042257 A CN2012103042257 A CN 2012103042257A CN 201210304225 A CN201210304225 A CN 201210304225A CN 102856337 A CN102856337 A CN 102856337A
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Abstract
The invention relates to a pixel unit, which comprises a substrate, a silicon oxide layer and a silicon nitride layer, wherein the substrate is provided with a light-sensitive area, and the silicon oxide layer and the silicon nitride layer are arranged on the light-sensitive area from bottom to top. In addition, the invention also provides a manufacturing method of the pixel unit and a CMOS (complementary metal oxide semiconductor) image sensor comprising the pixel unit. By adopting the technical scheme, the problem of over high dark current of the pixel unit can be better solved, and the problem of poor sensitivity of the CMOS image sensor comprising the pixel unit can also be solved.
Description
Technical field
The present invention relates to semiconductor applications, particularly a kind of pixel cell and preparation method thereof, comprise the cmos image sensor of this pixel cell.
Background technology
The effect of imageing sensor is that optical imagery is converted into the corresponding signal of telecommunication.Imageing sensor is divided into CMOS (Complementary Metal Oxide Semiconductor) (CMOS) imageing sensor and charge-coupled device (CCD) imageing sensor.The advantage of ccd image sensor is higher to the image susceptibility, and noise is little, but the integrated relatively difficulty of ccd image sensor and other devices, and also the power consumption of ccd image sensor is higher.By contrast, cmos image sensor have technique simple, easily and other devices are integrated, volume is little, lightweight, power consumption is little, low cost and other advantages.Cmos image sensor has been widely used in static digital camera, camera cell phone, Digital Video, medical camera head (such as gastroscope), automobile-used camera head etc. at present.
The parts that in the cmos image sensor optical imagery are converted into the corresponding signal of telecommunication are pixel cell.With reference to shown in Figure 1, pixel cell comprises photosensitive unit 11 and image element circuit zone 12.Fig. 2 is the sectional structure schematic diagram along the A-A straight line among Fig. 1.Can find out that photosensitive unit 11 is formed with photosensitive region 111, pixel cell is formed with the transistor 121 that electric signal transmission that photosensitive unit 11 is converted to is gone out.In addition, be subjected to the pollution of steam in successive process or the use procedure etc. for preventing photosensitive region 111, be formed with preferably silicon nitride layer 13 of one deck compactness in this Semiconductor substrate that comprises photosensitive region 111.As required, be formed with metal interconnect structure on the follow-up transistor 121, be formed with filter element and lenticule etc. on the photosensitive region 111.
Yet above-mentioned pixel cell in use has the excessive problem of dark current, and correspondingly, the cmos image sensor that comprises this pixel cell has the relatively poor problem of sensitivity.
For the reason that the problems referred to above produce, be commonly considered as that defective by photosensitive region 111 causes.In order to improve defects, prior art also has some schemes to be suggested.For example when forming transistor 121 and metal interconnect structure, form the through hole that the bottom is positioned at the interface of Semiconductor substrate and silicon nitride layer 13 in image element circuit zone 12 simultaneously, and in this through hole, pass into hydrogen, the bound not strong characteristics of its free electron are improved the defective of photosensitive region 111 to utilize hydrogen atom in the hydrogen.
But such scheme to improve effect very limited.
Summary of the invention
The problem that the present invention solves is the cmos image sensor that proposes a kind of new pixel cell and preparation method thereof, comprises this pixel cell, improve preferably the excessive problem of dark current of pixel cell, and comprise the relatively poor problem of sensitivity of the cmos image sensor of this pixel cell.
For addressing the above problem, the invention provides a kind of pixel cell, comprising:
Substrate with photosensitive region;
Be positioned at the silicon oxide layer on the described photosensitive region;
Be positioned at the silicon nitride layer on the described silicon oxide layer.
Alternatively, the thickness range of described silicon oxide layer is: 50 microns-500 microns.
Alternatively, the thickness range of described silicon nitride layer is: 100 microns-500 microns.
Alternatively, described substrate comprises Semiconductor substrate, is positioned at the epitaxial loayer of described semiconductor substrate surface.
Alternatively, described substrate has a plurality of photosensitive regions, between the adjacent photosensitive region by shallow trench isolation from.
Alternatively, the substrate that closes on described photosensitive region has transistor.
Alternatively, described transistor is transfering transistor.
Alternatively, the doping ionic type of described photosensitive region is N-type or P type.
Based on above-mentioned pixel cell, the present invention also provides a kind of cmos image sensor that comprises above-mentioned pixel cell.
In addition, the present invention also provides the manufacture method of above-mentioned pixel cell, comprising:
Form photosensitive region in substrate;
Form silicon oxide layer at described photosensitive region;
Form silicon nitride layer at described silicon oxide layer;
Alternatively, forming photosensitive region in substrate forms by the doping Implantation.
Alternatively, the technique at substrate formation photosensitive region is selective epitaxial growth process and in-situ doped.
Alternatively, forming silicon oxide layer at described photosensitive region is to form by chemical vapour deposition (CVD) formation or selective oxidation method.
Alternatively, when forming silicon oxide layer, described photosensitive region also forms the part of the transistorized grid oxic horizon of close region.
Compared with prior art, the present invention has the following advantages: 1) existing scheme is by forming through hole processes to improve photosensitive region to the interface of Semiconductor substrate and silicon nitride layer defective in the image element circuit zone, but this photosensitive region is covered by the silicon nitride layer of densification, thereby it is limited to improve effect.Be different from such scheme, the present invention proposes between photosensitive region and silicon nitride layer silicon oxide layer to be set, and when avoiding silicon nitride layer directly to contact with photosensitive region, defective appears in the surface of causing excessively by force photosensitive region to contact with it owing to the silicon nitride layer adhesion.
2) in the possibility, the formation method of silicon oxide layer is chemical vapour deposition technique or selective oxidation method, with respect to the selective oxidation method, chemical vapour deposition technique does not use the thickness of the photosensitive region of former substrate, thereby, this photosensitive region still can be made according to the specifications parameter of former pixel unit, so that this programme and existing processing compatibility are good.
3) in the possibility, the thickness range of described silicon oxide layer is: 50 microns-500 microns, the thickness range of silicon nitride layer is: 100 microns-500 microns, and namely avoided the defective of photosensitive region to produce, realized again photosensitive region completely cut off the pollutions such as steam.
4) in the possibility, the substrate that closes on described photosensitive region has transistor, and namely the image element circuit zone has the transistor of realizing transfer, selection etc., forms simultaneously the part of this transistorized grid oxic horizon when photosensitive region forms oxide layer.
Description of drawings
Fig. 1 is the vertical view of existing pixel cell;
Fig. 2 is the pixel cell partial cross section structural representation along A-A straight line among Fig. 1;
Fig. 3 is the circuit diagram of the 4T transistor pixel cell among the embodiment one;
Fig. 4 is the manufacture method flow chart of the pixel cell among the embodiment one;
Fig. 5 is the cross section structure schematic diagram of the pixel cell among the embodiment one;
Fig. 6 is the cross section structure schematic diagram of the pixel cell among the embodiment two.
Embodiment
For above-mentioned purpose of the present invention, feature and advantage can be become apparent more, below in conjunction with accompanying drawing the specific embodiment of the present invention is described in detail.
The inventor is in the dark current process of research pixel cell, find that reason that this dark current produces is not only that the defective of the existing photosensitive region that it is generally acknowledged produces, prior reason is relevant with the silicon nitride layer that forms on this photosensitive region surface in order to realize other pollutant such as isolated steam.Stronger to the outer-shell electron adsorptivity of other atom owing to nitrogen-atoms in this silicon nitride layer, easily cause silicon atom or other doped chemical of photosensitive region to lose electronics, this silicon or other doped chemical that loses electronics easily forms unsettled unsaturated bond, it is defective, this defective trapped electrons after light is converted into electronics, the number of electrons that impact is detected causes photoelectric conversion efficiency low.The problems referred to above when shining photosensitive region, can cause the larger problem of dark current unglazed.
For the problems referred to above, the present invention proposes between photosensitive region and the silicon nitride layer on it silicon oxide layer to be set, oxygen atom in this silicon oxide layer to the outer-shell electron adsorptivity of other atom a little less than, thereby, can not cause silicon atom or other doped chemical of photosensitive region to lose electronics, thereby avoid the defective generation.
The formation method of silicon oxide layer has two kinds, and a kind of is vapour deposition, adopts the extraneous method of introducing this layer, and another kind of is selective oxidation method (LOCOS), and the latter adopts existing suprabasil silicon to form silicon oxide layer.
Below take first method as example, introduce embodiments of the invention one.
Embodiment one
The structure that pixel cell in the CMOS graphical sensory device is commonly used has 3T transistor, 4T transistor.Below take the 4T transistor as example, the pixel cell that introduce to adopt technical scheme of the present invention to make.
With reference to the transistorized circuit diagram of 4T shown in Figure 3, its pixel cell 2 comprises: optical sensor 21, for generation of the electric charge of also collecting the light generation that is radiated on the photosensitive region; Transfering transistor 22 is used for the photoelectricity electric charge is transferred to sense node (being generally floating diffusion region 23) from optical sensor 21.Floating diffusion region 23 is electrically connected to the grid that transistor 24 is followed in the source.In addition, pixel cell 2 also comprises: reset transistor 25 is used for floating diffusion region 23 is reset to predetermined voltage V
DD Row selecting transistor 26 is for the response address signal and with signal V
OutFollow transistor 24 from the source and output to output.
The cross section structure schematic diagram of the flow chart that reference is shown in Figure 4 and pixel cell shown in Figure 5, at first execution in step S11 forms photosensitive regions 211 in substrate 20.
In the present embodiment, optical sensor 21 can be photodiode, such as PN junction, PIN knot etc.For forming photodiode, this substrate 20 is P type or N-type silicon substrate, correspondingly, defines well region in substrate 20, injects P type doping ion district or N-type doping ion district to form photosensitive region 211.The formation technique of above-mentioned photodiode is common process, and design parameter does not repeat them here with reference to existing parameter.
In addition, in concrete manufacturing process, this step forms a plurality of photosensitive regions 211 in substrate 20, isolates by shallow trench (STI) 27 between the adjacent photosensitive region 211.
Need to prove that the substrate 20 at the close region of photosensitive region 211 namely can form various transistors by other technique on the image element circuit zone, transfering transistor 22 as shown in Figure 5 and reset transistor 25.Thereby this step also forms each transistorized source-drain area (not indicating) in the image element circuit zone of substrate 20.
Then execution in step S12 still with reference to shown in Figure 5, forms silicon oxide layer 28 at described photosensitive region 211.
In the present embodiment, forming silicon oxide layer 28 at described photosensitive region 211 is to form by selective oxidation method (LOCOS).This selective oxidation method is common process, and the design parameter of formation can be with reference to existing technique.
As previously mentioned, the purpose that this step forms silicon oxide layer 28 is to utilize oxygen atom wherein not strong to the outer-shell electron absorption affinity of the silicon in the substrate 20 and other doping ion, be difficult for causing substrate 20, especially unsettled unsaturated bond appears in the surface of photosensitive region 211, has namely avoided the generation of defective.Simultaneously, based on the characteristic of this silicon oxide layer 28, its isolated effect to pollutants such as steam is good not as silicon nitride.Thereby, follow-uply on it also can form silicon nitride layer.The inventor finds that the thickness range of choice of silicon oxide layer 28 is: can better realize above-mentioned purpose in the time of 50 microns-500 microns.
Need to prove that the various transistors in image element circuit zone, transfering transistor 22 as shown in Figure 5 and the grid oxic horizon of reset transistor 25 also can be three layers of ONO structure of oxide-nitride thing-oxide.Thereby this step has formed the ground floor oxide of the transistorized grid oxic horizon in the substrate 20 of close region of photosensitive region 211 when forming silicon oxide layer 28.
Then execution in step S13 forms silicon nitride layer 29 at described silicon oxide layer 28.
The technique that forms silicon nitride layer 29 in this step can be the common process such as chemical vapour deposition (CVD), physical vapour deposition (PVD).The inventor finds that the thickness range of choice of silicon nitride layer 29 is: the purpose that can better realize the pollutants such as isolated steam in the time of 100 microns-500 microns.
In addition, this step has formed the second layer nitride of the transistorized grid oxic horizon in the substrate 20 of close region of photosensitive region 211 when forming silicon nitride layer 29.
Afterwards, the presumptive area on the surface of silicon nitride layer 29 forms other transistorized the 3rd layer of oxide (indicating), the grid (indicating) of image element circuit from bottom to top successively.Other transistor of pixel cell 2 etc. is finished by existing manufacture method.
So far, the pixel cell 2 of present embodiment one has been made complete.
To sum up, this pixel cell 2 comprises:
Be positioned at the silicon oxide layer 28 on the described photosensitive region 211;
Be positioned at the silicon nitride layer 29 on the described silicon oxide layer 28.
Based on above-mentioned pixel cell 2, present embodiment one also provides the cmos image sensor that comprises above-mentioned pixel cell 2.
Embodiment two
Pixel cell that present embodiment two provides and preparation method thereof is roughly the same with embodiment one.Difference is: as shown in Figure 6, this substrate 20 ' comprises injection N among the embodiment one or the Semiconductor substrate (silicon substrate) 20 of P type element, also comprises epitaxially grown epitaxial loayer 30 on it.The transistorized source-drain area in the image element circuit zone that photosensitive region 211, photosensitive region 211 close on all adopts the selective epitaxial growth method to be formed on this epitaxial loayer 30.In addition, the transistorized source-drain area in the image element circuit zone that photosensitive region 211, photosensitive region 211 close on is the limit growth, and the process of ion doping is carried out on the limit, i.e. in-situ doped technique.Above-mentioned in-situ doped technique can reduce the defective in the photosensitive region 211.
Embodiment three
Pixel cell that present embodiment three provides and preparation method thereof is roughly the same with embodiment one.Difference is: the silicon oxide layer 28 on the photosensitive region 211 is not to form by the LOCOS method, but forms by chemical vapour deposition technique.This chemical vapour deposition technique for example adopts silane and oxygen reaction to generate.
Be understandable that, the benefit of the method is: the thickness that needn't take established photosensitive region 211, like this, the sti structure 27 of the transistorized source-drain area in the image element circuit zone that photosensitive region 211, photosensitive region 211 close on, isolated each photosensitive region 211 is still made according to existing specifications parameter, thereby this method and existing processing compatibility are good.
Although the present invention with preferred embodiment openly as above; but it is not to limit the present invention; any those skilled in the art without departing from the spirit and scope of the present invention; can utilize method and the technology contents of above-mentioned announcement that technical solution of the present invention is made possible change and modification; therefore; every content that does not break away from technical solution of the present invention; to any simple modification, equivalent variations and modification that above embodiment does, all belong to the protection range of technical solution of the present invention according to technical spirit of the present invention.
Claims (14)
1. a pixel cell is characterized in that, comprising:
Substrate with photosensitive region;
Be positioned at the silicon oxide layer on the described photosensitive region;
Be positioned at the silicon nitride layer on the described silicon oxide layer.
2. pixel cell according to claim 1 is characterized in that, the thickness range of described silicon oxide layer is: 50 microns-500 microns.
3. pixel cell according to claim 1 is characterized in that, the thickness range of described silicon nitride layer is: 100 microns-500 microns.
4. pixel cell according to claim 1 is characterized in that, described substrate comprises Semiconductor substrate, is positioned at the epitaxial loayer of described semiconductor substrate surface.
5. pixel cell according to claim 1 is characterized in that, described substrate has a plurality of photosensitive regions, between the adjacent photosensitive region by shallow trench isolation from.
6. pixel cell according to claim 1 is characterized in that, the substrate that closes on described photosensitive region has transistor.
7. pixel cell according to claim 6 is characterized in that, described transistor is transfering transistor.
8. pixel cell according to claim 1 is characterized in that, the doping ionic type of described photosensitive region is N-type or P type.
9. a cmos image sensor is characterized in that, comprises the described pixel cell of claim 1 to 8 any one.
10. the manufacture method of a pixel cell is characterized in that, comprising:
Form photosensitive region in substrate;
Form silicon oxide layer at described photosensitive region;
Form silicon nitride layer at described silicon oxide layer;
11. manufacture method according to claim 10 is characterized in that, forms photosensitive region in substrate and forms by the doping Implantation.
12. manufacture method according to claim 10 is characterized in that, the technique that forms photosensitive region in substrate is selective epitaxial growth process and in-situ doped.
13. manufacture method according to claim 10 is characterized in that, forming silicon oxide layer at described photosensitive region is to form by chemical vapour deposition (CVD) formation or selective oxidation method.
14. manufacture method according to claim 10 is characterized in that, also forms the part of the transistorized grid oxic horizon of close region when described photosensitive region forms silicon oxide layer.
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| CN110707116A (en) * | 2019-10-17 | 2020-01-17 | 德淮半导体有限公司 | Image sensor unit |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101064328A (en) * | 2006-04-29 | 2007-10-31 | 联华电子股份有限公司 | Video sensing element and method for making the same |
| US20080224244A1 (en) * | 2007-03-14 | 2008-09-18 | Ryu Sang-Wook | Image sensor and method for manufacturing the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101064328A (en) * | 2006-04-29 | 2007-10-31 | 联华电子股份有限公司 | Video sensing element and method for making the same |
| US20080224244A1 (en) * | 2007-03-14 | 2008-09-18 | Ryu Sang-Wook | Image sensor and method for manufacturing the same |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110707116A (en) * | 2019-10-17 | 2020-01-17 | 德淮半导体有限公司 | Image sensor unit |
| CN110707116B (en) * | 2019-10-17 | 2021-08-24 | 德淮半导体有限公司 | Image sensor unit |
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