CN104269423A - Pixel structure of CMOS (Complementary Metal Oxide Semiconductor) image sensor - Google Patents
Pixel structure of CMOS (Complementary Metal Oxide Semiconductor) image sensor Download PDFInfo
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- CN104269423A CN104269423A CN201410594140.6A CN201410594140A CN104269423A CN 104269423 A CN104269423 A CN 104269423A CN 201410594140 A CN201410594140 A CN 201410594140A CN 104269423 A CN104269423 A CN 104269423A
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- photodiode
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Abstract
The invention discloses a pixel structure of a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The pixel structure comprises a photoelectric diode, a charge transmission transistor, a reset transistor, a source following transistor, a selective transistor and a floating active area which are arranged in a semiconductor substrate, wherein a grid of the charge transmission transistor is manufactured in the semiconductor substrate; a P-type ion isolation area is arranged between the grid of the charge transmission transistor and the photoelectric diode. When the charge transmission transistor works, the direction of an electric field close to a channel of the charge transmission transistor points to the photoelectric diode from the grid of the charge transmission transistor, the electric potential in the direction of an electric field line is gradually reduced; in the process of switching the opened state into the closed state of the charge transmission transistor, electrons in the P-type ion isolation area and the channel of the charge transmission transistor only move in the opposite direction of the electric field line and cannot flow into the photoelectric diode, and the charge transmission transistor cannot make noise.
Description
Technical field
The present invention relates to field of image sensors, particularly a kind of CMOS image sensor pixel structure.
Background technology
Imageing sensor has been widely used in digital camera, cell phone, medicine equipment, automobile and other application scenarios.Particularly manufacture the fast development of CMOS (CMOS (Complementary Metal Oxide Semiconductor)) image sensor technologies, make the output image quality of people to imageing sensor have higher requirement.The basis material manufacturing image sensor devices is semiconductor silicon, but silicon is not perfect device material, can be attended by noise when devices function, and device noise have impact on the quality that imageing sensor gathers image.
In the prior art, the dot structure of cmos image sensor, as shown in Figure 1, comprises the floor map two parts in circuit diagram and dotted line frame.In Fig. 1, the components and parts of shown pixel comprise: photodiode 101, charge pass transistor 102, reset transistor 103, source are followed transistor 104 and selected transistor 105, floating active area 106; VTX is the gate terminal of charge pass transistor 102, and VRX is the gate terminal of reset transistor 103, and VSX is the gate terminal selecting transistor 105, and Vdd is supply voltage, and Output is signal output part, and STI is shallow trench isolation region.Photodiode 101 receives extraneous incident light, produces photosignal; Open charge transistor 102, the photosignal in photodiode 101 is transferred to floating active area 106 district, follow by source floating active area 106 district potential well built-in potential variable signal that transistor 104 detects and to read through Output output and to preserve.
Charge pass transistor 102 of the prior art, when being in unlatching operating state, converges electric charge electronics to form conductive channel in its raceway groove; And charge pass transistor 102 is in the process of closing, its channel electrons can flow in photodiode 101 and floating active area 106 district simultaneously, as shown in Figure 1; But charge pass transistor is opened for more than 102 time and in the operation of closing, the quantity that each channel electrons flow in photodiode 101 can not be equal, the quantity flowing into floating active area 106 district also can not be equal, and this unequal electron amount defines the device noise of charge pass transistor 102.Device noise in pixel is obscured in picture signal, and make the picture signal collected can not reflect real information in kind, the material picture particularly under half-light environment thickens unclear.
Summary of the invention
The object of this invention is to provide a kind of efficiently, reduce the CMOS image sensor pixel structure of device noise.
The object of the invention is to be achieved through the following technical solutions:
CMOS image sensor pixel structure of the present invention, comprise the photodiode, charge pass transistor, reset transistor, the source that are placed in semiconductor substrate to follow transistor, select transistor, floating active area, the fabrication of described charge pass transistor is inner at described semiconductor substrate, is provided with P type ionic isolation district between the grid of described charge pass transistor and described photodiode.
As seen from the above technical solution provided by the invention, the CMOS image sensor pixel structure that the embodiment of the present invention provides, because the fabrication of the charge pass transistor in pixel is inner at semiconductor substrate, and between charge transfer transistor gate and photodiode, be provided with P type ionic isolation district, during described charge pass transistor work, direction of an electric field near its raceway groove points to photodiode by charge transfer transistor gate, and the electromotive force along electric field line direction reduces gradually; Charge pass transistor is transformed into closed condition process from opening, electronics in P type ionic isolation district and charge pass transistor raceway groove can only move along the opposite direction of electric field line, and can not flow in photodiode, the charge pass transistor therefore in dot structure of the present invention can not produce noise.
Accompanying drawing explanation
Fig. 1 is the CMOS image sensor pixel structure schematic diagram of prior art.
Fig. 2 is the dot structure schematic diagram of cmos image sensor of the present invention.
Fig. 3 is the tangent plane schematic diagram of the position of tangent line 1 shown in Fig. 2 in CMOS image sensor pixel structure of the present invention.
Fig. 4 is the tangent plane schematic diagram of the position of tangent line 2 shown in Fig. 2 in CMOS image sensor pixel structure of the present invention.
Fig. 5 be CMOS image sensor pixel structure of the present invention carry out Charger transfer operation time, the tangent plane schematic diagram of the position of tangent line 1 shown in Fig. 2.
Fig. 6 be CMOS image sensor pixel structure of the present invention carry out Charger transfer operation time, the planar section schematic diagram of photodiode and charge pass transistor.
Fig. 7 be CMOS image sensor pixel structure of the present invention carry out Charger transfer operation time, the potential well schematic diagram of the position of tangent line 3 shown in Fig. 6.
Embodiment
To be described in further detail the embodiment of the present invention below.
CMOS image sensor pixel structure of the present invention, its preferably embodiment be:
Comprise the photodiode, charge pass transistor, reset transistor, the source that are placed in semiconductor substrate to follow transistor, select transistor, floating active area, the fabrication of described charge pass transistor is inner at described semiconductor substrate, is provided with P type ionic isolation district between the grid of described charge pass transistor and described photodiode.
Distance between the grid of described charge pass transistor and photodiode is more than or equal to 0.2um, the grid of described charge pass transistor is more than or equal to 0.3um with the parallel crossover region between photodiode, and the degree of depth of grid in semiconductor substrate of described charge pass transistor is more than or equal to 0.3um.
Polysilicon sidewall and the bottom of described charge transfer transistor gate are provided with thin oxide layer, and the thickness of described thin oxide layer is 3nm ~ 15nm.
The side in described P type ionic isolation district contacts with described photodiode, the overlapping 0um ~ 0.2um of grid of opposite side and described charge pass transistor, and the degree of depth in described P type ionic isolation district is greater than the described charge transfer transistor gate degree of depth at least 0.1um.
Be provided with P type ionic isolation district between described floating active area and photodiode, the distance of described floating active area and photodiode is more than or equal to 0.2um.
Grid and the floating active area of described charge pass transistor are manufactured with P well region, and described P well region contacts with P type ionic isolation district.
Described photodiode is N-type photodiode, and described charge pass transistor, reset transistor, source follow transistor, selection transistor is N-type transistor.
The P type ion concentration in described P type ionic isolation district is 1E15Atom/cm
3~ 1E17Atom/cm
3.
CMOS image sensor pixel structure of the present invention, because the fabrication of the charge pass transistor in pixel is inner at semiconductor substrate, and between charge transfer transistor gate and photodiode, be provided with P type ionic isolation district, during described charge pass transistor work, direction of an electric field near its raceway groove points to photodiode by charge transfer transistor gate, and the electromotive force along electric field line direction reduces gradually; Charge pass transistor is transformed into closed condition process from opening, electronics in P type ionic isolation district and charge pass transistor raceway groove can only move along the opposite direction of electric field line, and can not flow in photodiode, the charge pass transistor therefore in dot structure of the present invention can not produce noise.
Specific embodiment:
As shown in Figure 2, the planar section in dotted line frame and the circuit part schematic diagram outside dotted line frame is comprised.In Fig. 2,201 is photodiode, and 202 is charge pass transistor, and 203 is reset transistor, 204 for following transistor in source, and 205 for selecting transistor, and Output is signal output part, 206 is floating active area, and 207 is P type ionic isolation district, and 208 is thin oxide layer; STI is shallow trench isolation region, and P well region is the P Xing Jing ion district of logic process, and contact hole is metal wire and active area or the tie point with transistor gate, and Vdd is supply voltage, and tangent line 1 and tangent line 2 characterize two tangent plane positions.Shown in Fig. 2, Vtx is the gate terminal of charge pass transistor 202, and Vrst is the gate terminal of reset transistor 203, and Vsx is the gate terminal selecting transistor 205.P type ionic isolation district is provided with between the grid of described charge pass transistor 202 and photodiode 201, distance between the grid of described charge pass transistor 202 and photodiode 201 is more than or equal to 0.2um, the grid of described charge pass transistor 202 is more than or equal to 0.3um with the parallel crossover region between photodiode 201, the grid of described charge pass transistor 202 and floating active area 206 make does P well region, and described P well region contacts with P type ionic isolation district.Described photodiode 201 is N-type photodiode, and described charge pass transistor 202, reset transistor 203, source are followed transistor 204, selected transistor 205 for N-type transistor.
The tangent plane schematic diagram of the position of tangent line 1 shown in Fig. 2, as shown in Figure 3, wherein photodiode 201, P type ionic isolation district 207, the grid of charge pass transistor 202, thin oxide layer 208, P well region are produced on semiconductor substrate inside.Shown in Fig. 3, the left side in described P type ionic isolation district 207 contacts with photodiode, 0um ~ 0.2um overlapping with the grid of charge pass transistor on the right side of it, and the P type ion concentration in described P type ionic isolation district 207 is 1E15Atom/cm3 ~ 1E17Atom/cm3; The degree of depth of grid in semiconductor substrate of described charge pass transistor 202 is more than or equal to 0.3um; The degree of depth in described P type ionic isolation district 207 is more than or equal to charge pass transistor 202 gate depth at least 0.1um; Described thin oxide layer 208 is positioned at sidewall and the diapire of charge pass transistor 202 grid, and its thickness is 3nm ~ 15nm; Shallow trench isolation region STI is positioned at the right side of charge pass transistor 202; Described P well region connects with P type ionic isolation district 207.
The tangent plane schematic diagram of the position of tangent line 2 shown in Fig. 2, as shown in Figure 4, the left side in P type ionic isolation district 207 is photodiode 201, it is floating active area 206 on the right side of it, and floating active area 206 is produced on P well region, the right side of described floating active area 206 is shallow trench isolation region STI, connects on the left of described P well region with P type ionic isolation district 207.The distance at least 0.2um of described floating active area 206 and charge pass transistor 201.
Pixel operation feature of the present invention is elaborated further below in conjunction with accompanying drawing 5 ~ accompanying drawing 7.When cmos image sensor pixel of the present invention carries out Charger transfer operation, the tangent plane schematic diagram of the position of tangent line 1 shown in Fig. 2 as figure 5 illustrates.Shown in Fig. 5, the gate terminal Vtx of charge pass transistor 202 is high potential Vdd, the grid of charge pass transistor 202 near its raceway groove, P type ionic isolation district 207 and induce electric field near photodiode 201 district in P type ionic isolation district 207, its direction of an electric field points to photodiode 201 from the grid of charge pass transistor 202, according to electromagnetic theory, its electromotive force of direction along electric field line reduces gradually, and the electronics therefore in photodiode 201 moves to the silicon face near thin oxide layer 208 along the opposite direction of electric field line from photoelectric diode 201.
When cmos image sensor pixel of the present invention carries out Charger transfer operation, the planar section schematic diagram of photodiode 201 and charge pass transistor 202, as shown in Figure 6, the electromotive force of the gate terminal Vtx of charge pass transistor 202 is high potential Vdd, and tangent line 3 characterizes position.Electronics in photodiode 201 is along the direction of electric field line from photodiode 201, stride across P type ionic isolation district 207, move to the silicon face near thin oxide layer 208, because the electromotive force of floating active area 206 is the highest, the electrons of the silicon face near thin oxide layer 208 continues to flow into floating active area 206 district, as shown in Figure 6.
When cmos image sensor pixel of the present invention carries out Charger transfer operation, the potential well schematic diagram of the position of tangent line 3 shown in Fig. 6 as shown in Figure 7, wherein, 701 is the potential well area of photodiode 201,702 is the potential well area in P type ionic isolation district 207,703 is the potential well area of floating active area 206, potential lines 1 is the potential energy diagram of charge pass transistor 202 when being in opening, potential lines 2 is that charge pass transistor 202 is set to the potential energy diagram closed condition process from opening, and potential lines 3 is the potential energy diagram of charge pass transistor 202 when being in closed condition.Shown in Fig. 7, when charge pass transistor 202 is in opening, i.e. potential lines 1 state, the electronics of 701 potential well areas flows into 702 potential well areas of high potential, and then flows into 703 potential well areas of more high potential, and electronics is finally collected at 703 potential well areas; 702 potential well areas, the electromotive force of potential lines 1 and potential lines 2 raises gradually along with away from 701 potential well areas, reaches peak at the raceway groove place electromotive force of charge pass transistor 202.As can be seen here, the electronics of 702 potential well areas, can not flow into 701 potential well areas, can only flow into 703 potential well areas of high potential.So, charge pass transistor 202 in dot structure of the present invention can not produce noise, effectively reduce the pixel noise of imageing sensor, detailed information in kind under adopting the imageing sensor of present invention pixel to collect more half-light environment, and then effectively improve the image quality of imageing sensor collection.
The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.
Claims (8)
1. a CMOS image sensor pixel structure, comprise the photodiode, charge pass transistor, reset transistor, the source that are placed in semiconductor substrate to follow transistor, select transistor, floating active area, it is characterized in that, the fabrication of described charge pass transistor is inner at described semiconductor substrate, is provided with P type ionic isolation district between the grid of described charge pass transistor and described photodiode.
2. CMOS image sensor pixel structure according to claim 1, it is characterized in that, distance between the grid of described charge pass transistor and photodiode is more than or equal to 0.2um, the grid of described charge pass transistor is more than or equal to 0.3um with the parallel crossover region between photodiode, and the degree of depth of grid in semiconductor substrate of described charge pass transistor is more than or equal to 0.3um.
3. CMOS image sensor pixel structure according to claim 2, is characterized in that, polysilicon sidewall and the bottom of described charge transfer transistor gate are provided with thin oxide layer, and the thickness of described thin oxide layer is 3nm ~ 15nm.
4. CMOS image sensor pixel structure according to claim 3, it is characterized in that, the side in described P type ionic isolation district contacts with described photodiode, overlapping 0um ~ the 0.2um of grid of opposite side and described charge pass transistor, the degree of depth in described P type ionic isolation district is greater than the described charge transfer transistor gate degree of depth at least 0.1um.
5. CMOS image sensor pixel structure according to claim 4, is characterized in that, is provided with P type ionic isolation district between described floating active area and photodiode, and the distance of described floating active area and photodiode is more than or equal to 0.2um.
6. CMOS image sensor pixel structure according to claim 5, is characterized in that, grid and the floating active area of described charge pass transistor are manufactured with P well region, and described P well region contacts with P type ionic isolation district.
7. CMOS image sensor pixel structure according to claim 6, is characterized in that, described photodiode is N-type photodiode, and described charge pass transistor, reset transistor, source follow transistor, selection transistor is N-type transistor.
8. the CMOS image sensor pixel structure according to any one of claim 1 to 7, is characterized in that, the P type ion concentration in described P type ionic isolation district is 1E15Atom/cm
3~ 1E17Atom/cm
3.
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| CN201410594140.6A CN104269423A (en) | 2014-10-29 | 2014-10-29 | Pixel structure of CMOS (Complementary Metal Oxide Semiconductor) image sensor |
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Cited By (1)
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| CN111199987A (en) * | 2018-11-19 | 2020-05-26 | 力晶科技股份有限公司 | Image sensor and method for manufacturing the same |
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Patent Citations (5)
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| CN1812112A (en) * | 2004-10-20 | 2006-08-02 | 三星电子株式会社 | Solid image sensor device with nonplanar transistor and manufacture method thereof |
| US20100328509A1 (en) * | 2006-08-08 | 2010-12-30 | Canon Kabushiki Kaisha | Photoelectric conversion apparatus, control method thereof, imaging apparatus, and imaging system |
| CN101359675A (en) * | 2007-08-03 | 2009-02-04 | 夏普株式会社 | Solid state image capture device, manufacture method thereof and electronic information device |
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| CN111199987A (en) * | 2018-11-19 | 2020-05-26 | 力晶科技股份有限公司 | Image sensor and method for manufacturing the same |
| CN111199987B (en) * | 2018-11-19 | 2022-09-06 | 力晶积成电子制造股份有限公司 | Image sensor and method for manufacturing the same |
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Application publication date: 20150107 |