CN112447775A - CMOS image sensor pixel manufacturing method for improving quantum efficiency - Google Patents
CMOS image sensor pixel manufacturing method for improving quantum efficiency Download PDFInfo
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 8
- 239000000758 substrate Substances 0.000 claims abstract description 18
- 239000004065 semiconductor Substances 0.000 claims abstract description 10
- 150000002500 ions Chemical class 0.000 claims abstract description 5
- 230000007935 neutral effect Effects 0.000 claims description 8
- 230000005540 biological transmission Effects 0.000 claims description 6
- 238000005468 ion implantation Methods 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 4
- 230000005684 electric field Effects 0.000 claims description 3
- 238000005516 engineering process Methods 0.000 claims description 2
- 238000003384 imaging method Methods 0.000 abstract description 6
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- 238000009792 diffusion process Methods 0.000 description 6
- 238000010521 absorption reaction Methods 0.000 description 1
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- 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
- H01L27/14601—Structural or functional details thereof
- H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
- H01L27/1461—Pixel-elements with integrated switching, control, storage or amplification elements characterised by the photosensitive area
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- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
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- H01L27/144—Devices controlled by radiation
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- H01L27/14643—Photodiode arrays; MOS imagers
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Abstract
A method for manufacturing a CMOS image sensor pixel capable of improving quantum efficiency adopts a method of injecting high-concentration P-type ions into the back of the pixel and exhausting a thicker sensitive semiconductor area by applying reverse bias on a substrate, so that a field-free area is eliminated, and photo-generated charges are collected quickly. The magnitude of the reverse bias depends on the resistivity and thickness of the semiconductor substrate and can far exceed any other voltage in the system. Finally, the quantum efficiency of the image sensor is further improved, and the imaging quality is greatly improved.
Description
Technical Field
The invention belongs to the field of CMOS image sensors, and particularly relates to a CMOS image sensor pixel manufacturing method for improving quantum efficiency, wherein incident light is in a near-infrared or soft X-ray waveband.
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.
For incident light in the near infrared and X-ray bands of longer wavelengths, the absorption length can reach tens or even hundreds of microns. The PPD type 4T pixel using the conventional CMOS image sensor cannot reach such a deep depletion region depth, thereby causing a low quantum efficiency and reducing an imaging performance of the image sensor. In the pixel epitaxial layer, the parts except the depletion layer are neutral regions, and if incident light is absorbed in the neutral regions and photo-generated electron-hole pairs are generated, signal charges cannot be transferred to the floating diffusion nodes and finally cannot be successfully read out.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a CMOS image sensor pixel manufacturing method capable of improving quantum efficiency. The magnitude of the reverse bias depends on the resistivity and thickness of the semiconductor substrate and can far exceed any other voltage in the system. Finally, the quantum efficiency of the image sensor is further improved, and the imaging quality is greatly improved.
A CMOS image sensor pixel manufacturing method for improving quantum efficiency is disclosed, as shown in FIG. 2, firstly, a high-concentration P-type ion implantation is performed at the bottom of a substrate before a gate is formed, a P + + region is formed, namely, a depletion region 2 is added in a neutral region below an original PPD region. 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 perform deep P-type ion implantation once before the gate is formed, and the substrate applies negative pressure, so that the two formed depletion regions are connected. When light with longer wavelength irradiates a PPD region, electrons in a valence band in a semiconductor material absorb the energy of photons, and the energy passes through a forbidden band from the valence band to reach a conduction band, so that a photogenerated electron-hole pair, namely a photogenerated carrier, is formed, and the photogenerated electrons are collected in the PPD region and the photogenerated holes are absorbed by a substrate under the action of an electric field in a depletion region; the photo-generated charge generated by photons absorbed in the neutral region at the bottom of the depletion region cannot be collected by the PPD region.
Compared with the traditional 4T active pixel, the pixel manufacturing method provided by the invention has the advantages that the heavily doped P-type ion implantation is added at the bottom of the substrate, the negative voltage is applied, so that depletion regions formed by the PPD and the substrate as well as the substrate and the heavily doped P-type region are connected, the depth of the depletion region is increased equivalently finally, when light with longer wavelength irradiates the PPD region, photo-generated charges are absorbed by the formed deep depletion region and are transferred to the floating diffusion node end at the conduction stage of the transmission tube and are read out finally, the collection rate and the quantum efficiency of the photo-generated charges are effectively improved, and the imaging quality of the sensor is improved.
Drawings
FIG. 1 is a basic structure diagram of a 4T pixel;
fig. 2 shows a pixel structure with the addition of P + + ion implantation at the bottom of the substrate.
Detailed Description
The present invention will be described in detail below with reference to the drawings and examples.
According to the invention, a P + + region is formed by carrying out high-concentration P-type ion implantation at the bottom of a substrate once, a depletion region 2 is added in a neutral region below an original PPD region, the doping concentrations of an epitaxial layer and the P + + region and negative voltage applied by the substrate are well controlled, so that the depletion region 1 and the depletion region 2 can be connected together to form a complete depletion region, photogenerated charges generated by near infrared rays or soft X rays at a deep position are collected in the depletion region and are transmitted to a floating diffusion node through a transmission tube, and finally read out. The structure can effectively improve the quantum efficiency and further improve the imaging quality of the image sensor.
The CMOS image sensor pixel structure for improving the quantum efficiency is suitable for pixels of which incident light is near infrared rays or soft X rays in a longer wave band, and the PPD depletion region 1 is connected with the depletion region 2 formed by the substrate and the epitaxial layer. For example, for a pixel with near infrared light as incident light, a P-type epitaxial layer is formed by doping B ions with 2e13/cm2, a heavily doped P + + region is formed at the bottom of the substrate by implanting B ions with a concentration of 1e15/cm2, and a negative voltage of-4.0V is applied to the substrate. The depth of a depletion region 1 formed by PPD and a P-type epitaxial layer can reach 3 um; the P + + layer forms a depletion region with the epitaxial layer having a depth in the range of about 10um to about 15 um. For the pixel with the epitaxial thickness of 12um, the depletion region 1 and the depletion region 2 formed according to the process conditions are overlapped in space, so that the photosensitive area is effectively increased, and further the quantum 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 of low neutral region diffused dark current can be realized on the basis of ensuring a large photosensitive area.
Claims (1)
1. A CMOS image sensor pixel manufacturing method for improving quantum efficiency is characterized by comprising the following steps: firstly, carrying out high-concentration P-type ion implantation at the bottom of a substrate before forming a gate to form a P + + region, namely adding a depletion region in a neutral region below an original PPD region, and applying negative pressure to the substrate to connect the two depletion regions; after the transmission gate is formed, injecting N-type ions by adopting a self-alignment technology to form an N-photosensitive area and an FD area of PPD; when light with longer wavelength irradiates a PPD region, electrons in a valence band in a semiconductor material absorb the energy of photons, and the energy passes through a forbidden band from the valence band to reach a conduction band, so that a photogenerated electron-hole pair, namely a photogenerated carrier, is formed, and the photogenerated electrons are collected in the PPD region and the photogenerated holes are absorbed by a substrate under the action of an electric field in a depletion region; the photo-generated charge generated by photons absorbed in the neutral region at the bottom of the depletion region cannot be collected by the PPD region.
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| CN1481585A (en) * | 2000-10-19 | 2004-03-10 | ���Ӱ뵼������˾ | Method of fabricating heterojunction photodiodes integrated with CMOS |
| US20050167711A1 (en) * | 2003-06-16 | 2005-08-04 | Chandara Mouli | Photodiode with ultra-shallow junction for high quantum efficiency CMOS image sensor and method of formation |
| TW200926033A (en) * | 2007-07-18 | 2009-06-16 | Steven Kays | Adaptive electronic design |
| CN102376730A (en) * | 2010-08-20 | 2012-03-14 | 美商豪威科技股份有限公司 | Entrenched transfer gate |
| CN103400872A (en) * | 2013-06-30 | 2013-11-20 | 北京工业大学 | Structure and preparation method of surface electric field enhanced PIN photoelectric detector |
| CN104112782A (en) * | 2014-07-23 | 2014-10-22 | 中国航天科技集团公司第九研究院第七七一研究所 | Anti-crosstalk reverse-U-shaped buried layer photodiode and generation method |
| US9991309B1 (en) * | 2017-07-05 | 2018-06-05 | Omnivision Technologies, Inc. | CMOS image sensor having enhanced near infrared quantum efficiency |
| CN108493206A (en) * | 2018-04-27 | 2018-09-04 | 上海集成电路研发中心有限公司 | A kind of cmos image sensor improving quantum efficiency |
-
2019
- 2019-08-28 CN CN201910801765.8A patent/CN112447775A/en active Pending
Patent Citations (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6180969B1 (en) * | 1998-02-28 | 2001-01-30 | Hyundai Electronics Industries Co., Ltd. | CMOS image sensor with equivalent potential diode |
| GB9915187D0 (en) * | 1998-06-29 | 1999-09-01 | Hyundai Electronics Ind | Photodiode having charge function and image sensor using the same |
| KR20000010196A (en) * | 1998-07-30 | 2000-02-15 | 김영환 | Photo-diod with image sensor |
| CN1481585A (en) * | 2000-10-19 | 2004-03-10 | ���Ӱ뵼������˾ | Method of fabricating heterojunction photodiodes integrated with CMOS |
| US20050167711A1 (en) * | 2003-06-16 | 2005-08-04 | Chandara Mouli | Photodiode with ultra-shallow junction for high quantum efficiency CMOS image sensor and method of formation |
| TW200926033A (en) * | 2007-07-18 | 2009-06-16 | Steven Kays | Adaptive electronic design |
| CN102376730A (en) * | 2010-08-20 | 2012-03-14 | 美商豪威科技股份有限公司 | Entrenched transfer gate |
| CN103400872A (en) * | 2013-06-30 | 2013-11-20 | 北京工业大学 | Structure and preparation method of surface electric field enhanced PIN photoelectric detector |
| CN104112782A (en) * | 2014-07-23 | 2014-10-22 | 中国航天科技集团公司第九研究院第七七一研究所 | Anti-crosstalk reverse-U-shaped buried layer photodiode and generation method |
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