CN112447776A - CMOS image sensor pixel manufacturing method capable of reducing charge backflow - Google Patents
CMOS image sensor pixel manufacturing method capable of reducing charge backflow Download PDFInfo
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- CN112447776A CN112447776A CN201910801787.4A CN201910801787A CN112447776A CN 112447776 A CN112447776 A CN 112447776A CN 201910801787 A CN201910801787 A CN 201910801787A CN 112447776 A CN112447776 A CN 112447776A
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 9
- 238000009792 diffusion process Methods 0.000 claims abstract description 16
- 150000002500 ions Chemical class 0.000 claims abstract description 10
- 230000005540 biological transmission Effects 0.000 claims description 9
- 238000005516 engineering process Methods 0.000 claims description 2
- 238000002347 injection Methods 0.000 claims description 2
- 239000007924 injection Substances 0.000 claims description 2
- 238000003384 imaging method Methods 0.000 abstract description 6
- 238000002513 implantation Methods 0.000 abstract description 4
- 230000008859 change Effects 0.000 abstract description 2
- 238000000034 method Methods 0.000 description 7
- 230000008569 process Effects 0.000 description 6
- 238000005468 ion implantation Methods 0.000 description 5
- 239000004065 semiconductor Substances 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- 230000009471 action Effects 0.000 description 2
- 238000010351 charge transfer process Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 206010070834 Sensitisation Diseases 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000007943 implant Substances 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000005036 potential barrier Methods 0.000 description 1
- 230000008313 sensitization Effects 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
- H01L27/14689—MOS based technologies
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Abstract
A CMOS image sensor pixel manufacturing method capable of reducing charge backflow includes the steps that P-type ions are implanted twice before a grid is formed, the implantation dosage is gradually reduced from a PPD end to a floating diffusion node end, a P-type doping area with gradient concentration change is formed, more charges in a channel flow to one end of the floating diffusion node, the phenomenon that the charges flow back to the PPD end is effectively reduced, and charge transfer efficiency and imaging quality are greatly improved.
Description
Technical Field
The invention relates to the field of CMOS image sensors, in particular to a CMOS image sensor pixel manufacturing method capable of reducing charge backflow.
Background
A clamped photodiode (PPD) was originally used in a CCD image sensor, and was used in a CMOS image sensor over twenty years later. Fig. 1 is a PPD-based 4T pixel structure. The 4T pixel is composed of a PPD, a transmission tube, a reset tube, a row gate tube and a floating diffusion node. When light is incident on the semiconductor surface, a portion of the incident light is reflected and the remainder is absorbed by the semiconductor. When the photon energy entering the semiconductor is not lower than the forbidden bandwidth of the semiconductor material, the semiconductor material absorbs the energy with a certain probability, so that electron-hole pairs, namely photon-generated carriers, are generated. After illumination integration is completed, the transmission tube is conducted, photo-generated charges are transferred to the floating diffusion node from the photodiode region under the action of an electric field, namely, the charge-voltage information conversion process is completed, and finally, optical signals stored in the floating diffusion node are read out line by line through the line gate tube and the column-level reading circuit.
Aiming at the problem of charge backflow existing beyond the existing method for improving the charge transfer efficiency by reducing or eliminating potential barrier potential wells in the charge transfer process, namely that in the process of transferring photo-generated charges from PPD to FD in the state that a transfer tube is opened, due to the fact that strong light generates a large signal, the photo-generated charges overflow from an FD region to a channel under a transfer gate, as shown in fig. 2, when the transfer tube is in the conversion process from the opened state to the closed state, a part of the photo-generated charges stored under the gate flows back to the PPD, incomplete transfer of the charges is caused, and finally, an image tailing phenomenon is caused, and the imaging quality of an image sensor is reduced.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a CMOS image sensor pixel manufacturing method for reducing charge backflow, which comprises the steps of injecting P-type ions twice before forming a grid, gradually reducing the injection dosage from a PPD end to a floating diffusion node end, forming a P-type doping area with gradient concentration change, and enabling more charges in a channel to flow to one end of the floating diffusion node, thereby effectively reducing the phenomenon that the charges flow back to the PPD end, and greatly improving the charge transfer efficiency and the imaging quality.
A CMOS image sensor pixel manufacturing method for reducing charge backflow is disclosed, and connection and doping conditions of a PPD, a transmission gate and a floating diffusion node portion are shown in figure 3. Firstly, injecting P-type ions into a photosensitive area to form a P + clamping layer before forming a grid; after the transmission gate is formed, N-type ions are implanted by adopting a self-alignment technology to form an N-photosensitive area and an FD area of PPD. Compared with the traditional 4T active pixel, the pixel structure provided by the patent needs to implant P-type ions under the grid twice before the grid is formed, and the implantation dosage is gradually reduced from a PPD end to a floating diffusion node end and is respectively marked as PPPD_TGAnd PTG_FD。
The pixel manufacturing method of the P-type ion gradient doping under the grid provided by the invention enables the potential in the channel under the grid to be gradually increased from the PPD end to the floating diffusion end in the charge transfer process, so that more charges stored under the grid are transferred to the floating diffusion node end due to drift motion in the process of transferring the transfer tube from conduction to disconnection, the phenomenon that the charges flow back to the PPD end is effectively reduced, the charge transfer efficiency and the imaging quality are greatly improved, and the performance of a large input optical signal CMOS image sensor is improved.
Drawings
Fig. 1 is a basic structure diagram of a 4T pixel:
FIG. 2 is a diagram illustrating a charge backflow phenomenon; (transfer pipe in conducting state)
FIG. 3 is a two-dimensional pixel layout with two under-gate P-type ion implantations;
fig. 4 is a graph of the potential distribution with 2P-type ion implantations under the gate (the transfer tube is in the on state).
Detailed Description
The present invention will be described in detail below with reference to the drawings and examples.
The invention is formed by introducing two times of non-uniform P-type ion implantation into the channel under the transmission transistor gate before the gate is formedP PPD_TGAndP TG_FDand the area is formed by the area, so that more charges in the channel flow to the floating diffusion node end under the action of an electric field in the transition process of the transmission tube from the on state to the off state, the non-ideal effect of light-generated charges flowing back to PPD is equivalently reduced, the charge transfer efficiency of the pixel is effectively increased, and the imaging quality of the image sensor is improved.
A CMOS image sensor pixel manufacturing method capable of reducing charge backflow is suitable for pixels with low illumination and high conversion gain. By adopting the pixel structure provided by the patent, the quantity of photo-generated charges flowing back to a PPD area can be effectively reduced. For example, for a pixel with PPD size of 2 μm 5 μm, floating diffusion node conversion gain of 14 μ V/e-, and transfer tube gate length of 0.6 μm, P-type formed by doping with B ions of 1e13/cm2P PPD_TGRegion, P-type formed by B ion doping of 3e12/cm2P TG_FDThe implantation energy of the region is 80KeV, the implantation angle tilt is 7 degrees,P PPD_TGion implantation of regions andP TG_FDthe length of the overlapping region of the ion implantation mask of the region is 0.1 μm. The P-type doping concentration in the channel under the transmission tube gate formed according to the process conditions is gradually reduced from the PPD end to the floating diffusion node end, so that when the transmission tube is changed from a conducting state to a cutting-off state, the potential from the PPD end to the floating diffusion node end is gradually increased, the non-ideal effect that charges in the channel flow back to the PPD can be well reduced, and the charge transfer efficiency and the imaging quality of the image sensor are improved.
By adopting the pixel structure, structural optimization based on a PPD structure can be realized, and the pixel unit design for improving charge transfer efficiency by lower charge backflow is realized on the basis of ensuring high sensitization.
Claims (1)
1. A CMOS image sensor pixel manufacturing method for reducing charge backflow is characterized in that: firstly, before forming a grid, injecting P-type ions into a photosensitive area twice to form a P + clamping layer, wherein the injection dosage is gradually reduced from a PPD end to a floating diffusion node end and is respectively marked as PPPD_TGAnd PTG_FD(ii) a After the transmission gate is formed, N-type ions are implanted by adopting a self-alignment technology to form an N-photosensitive area and an FD area of PPD.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201910801787.4A CN112447776A (en) | 2019-08-28 | 2019-08-28 | CMOS image sensor pixel manufacturing method capable of reducing charge backflow |
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| CN201910801787.4A CN112447776A (en) | 2019-08-28 | 2019-08-28 | CMOS image sensor pixel manufacturing method capable of reducing charge backflow |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114141795A (en) * | 2021-06-08 | 2022-03-04 | 天津大学 | Manufacturing process of high conversion gain pixel |
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| KR20020057282A (en) * | 2000-12-30 | 2002-07-11 | 박종섭 | Image sensor capable of preventing flowing backward of charge |
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| CN102695008A (en) * | 2012-05-07 | 2012-09-26 | 天津大学 | CMOS image sensor pixel structure for fast transfer of large-size pixel charge |
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| CN103915457A (en) * | 2014-03-14 | 2014-07-09 | 复旦大学 | Silicon-based CMOS image sensor and method of the silicon-based CMOS image sensor for restraining photon-generated carrier surface trap recombination |
| CN104835825A (en) * | 2015-04-30 | 2015-08-12 | 湘潭大学 | High-speed CMOS image sensor |
-
2019
- 2019-08-28 CN CN201910801787.4A patent/CN112447776A/en active Pending
Patent Citations (9)
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|---|---|---|---|---|
| US4498013A (en) * | 1981-03-30 | 1985-02-05 | Matsushita Electric Industrial Co., Ltd. | Solid state image sensor exhibiting reduced image smearing effects |
| US4468852A (en) * | 1982-04-08 | 1984-09-04 | Sgs-Ates Componenti Elettronici S.P.A. | Process for making CMOS field-effect transistors with self-aligned guard rings utilizing special masking and ion implantation |
| KR20020057282A (en) * | 2000-12-30 | 2002-07-11 | 박종섭 | Image sensor capable of preventing flowing backward of charge |
| CN103400793A (en) * | 2006-05-31 | 2013-11-20 | 先进模拟科技公司 | Isolation structure for integrated circuit and modular method of forming same |
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|---|---|---|---|---|
| CN114141795A (en) * | 2021-06-08 | 2022-03-04 | 天津大学 | Manufacturing process of high conversion gain pixel |
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Application publication date: 20210305 |