CN109285851B - Pixel unit and preparation method thereof - Google Patents
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- 238000002360 preparation method Methods 0.000 title claims abstract description 9
- 239000000463 material Substances 0.000 claims abstract description 147
- 238000002955 isolation Methods 0.000 claims abstract description 53
- 238000009792 diffusion process Methods 0.000 claims abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 15
- 238000005530 etching Methods 0.000 claims abstract description 11
- 230000005540 biological transmission Effects 0.000 claims abstract description 8
- 229910021420 polycrystalline silicon Inorganic materials 0.000 claims abstract description 8
- 229920005591 polysilicon Polymers 0.000 claims abstract description 8
- 150000002500 ions Chemical class 0.000 claims description 15
- 239000000758 substrate Substances 0.000 claims description 10
- 238000001514 detection method Methods 0.000 claims description 7
- 150000001875 compounds Chemical class 0.000 claims description 6
- 229910021478 group 5 element Inorganic materials 0.000 claims description 6
- 230000003247 decreasing effect Effects 0.000 claims description 4
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- 239000007924 injection Substances 0.000 claims description 3
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- 230000000694 effects Effects 0.000 abstract description 4
- 239000002699 waste material Substances 0.000 abstract description 3
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- 210000000746 body region Anatomy 0.000 description 3
- 239000000969 carrier Substances 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- -1 boron ion Chemical class 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- HAYXDMNJJFVXCI-UHFFFAOYSA-N arsenic(5+) Chemical compound [As+5] HAYXDMNJJFVXCI-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
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- 238000002059 diagnostic imaging Methods 0.000 description 1
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- 238000005429 filling process Methods 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
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Abstract
The invention provides a pixel unit and a preparation method thereof, wherein the method comprises the following steps: step 1, injecting a P-type material into the edge of a P-type epitaxial layer surrounding a pixel unit to form an isolation region; step 2, forming a polysilicon gate on the upper surface of the P-type epitaxial layer, and etching the polysilicon gate to obtain a transmission gate; step 3, injecting N-type materials into the P-type epitaxial layer twice to form an N-type doped region; and 4, injecting an N-type material into the upper part of the P-type epitaxial layer to form a suspended diffusion node. The invention realizes the effect of inhibiting the body area crosstalk, reduces the area waste of pixel unit elements and pixel and logic circuit intervals, and effectively improves the filling factor.
Description
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to a pixel unit and a preparation method thereof.
Background
In recent years, the excellent characteristics of the near-infrared enhanced image sensor in the aspect of detection promote the wide application of the near-infrared enhanced image sensor, and the near-infrared enhanced image sensor is rapidly developed in the fields of medical imaging, laser radar, machine vision, intelligent transportation and the like. Especially in the field of laser radar ranging, near infrared light is often used as detection light for safety, so as to avoid damage to human eyes, and therefore, a photodiode receiving echo information is required to have good sensitivity to the near infrared light, so as to analyze the distance of a target object.
For the same kind of semiconductor material, the absorption coefficient and the incident depth are related to the wavelength of incident light, and the longer the wavelength is, the smaller the absorption coefficient is, the greater the incident depth is. For near infrared light of longer wavelength, sufficient depth is required for absorption. Therefore, the N-type doped region in the pixel unit needs to form a deeper junction depth so as to fully absorb near infrared light and improve the quantum efficiency.
In a pixel unit, a P-type substrate and a P-type epitaxial layer arranged on the P-type substrate are generally included, the thickness of the P-type epitaxial layer is generally about 10 μm, the depth of a depletion region formed in an N-type doped region of a photodiode is limited, and the absorption of near infrared light is difficult. To improve the absorption effect, the thickness of the epitaxial layer needs to be significantly increased to more than 20 μm to form a deeper PN junction. The increase of the junction depth causes the body area of the N-type doped region to be enlarged, the photo-generated carriers to be increased, and crosstalk among pixel units and between the pixel units and the logic circuit region is easily generated, so that the photo-generated carriers leak to an adjacent region during the charge integration period.
In order to avoid crosstalk between pixel units, a deep trench is usually etched between adjacent pixel units and then the isolation is formed by filling an insulating medium, and as the depth of the N-type doped region increases, the depth of the deep isolation trench also increases. However, the etching technology of the deep isolation trench with a high aspect ratio is an urgent problem to be solved in the current semiconductor integration, a steep sidewall is difficult to obtain in the deep etching process, the width of the trench is increased in order to achieve the required depth, especially the width of the trench opening is large, great waste is caused to the chip area, and the filling factor is reduced; in addition, the isolation mode needs to add etching and insulating medium filling processes in the process, the etching requirement of the deep groove on equipment is extremely high, common etching equipment cannot meet the requirement, special etching equipment is often required to be equipped, the process is complex, and the cost investment is increased.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a pixel unit and a preparation method thereof, and solves the problems of large groove width, complex process and high cost in the prior art.
In order to solve the technical problems, the invention adopts the following technical scheme:
a preparation method of a pixel unit comprises the following steps:
and 4, injecting an N-type material into the upper part of the P-type epitaxial layer to form a suspended diffusion node.
Further, the P-type material is a group III element ion or a compound of a group III element ion.
Further, in step 1, an isolation region is formed by implanting P-type material into the P-type epitaxial layer around the edge of the pixel cell, and the implantation at least includes two times of different energies.
Further, injecting P-type material into the P-type epitaxial layer surrounding the edge of the pixel unit four times in the step 1 to form an isolation region;
when the P-type material is implanted for four times, the energy of the P-type material implanted every time is sequentially increased, the dose of the P-type material implanted every time is the same, and the inclination of the P-type material implanted every time is the same.
Further, the step 1 of implanting P-type material into the P-type epitaxial layer around the edge of the pixel unit to form an isolation region includes:
for the first time: the energy of the implanted P-type material is 150 keV-300 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2The inclination when injecting the P-type material is 0-2 degrees;
and (3) for the second time: the energy of the implanted P-type material is 500 keV-700 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2The inclination when injecting the P-type material is 0-2 degrees;
and thirdly: the energy of the implanted P-type material is 1000 keV-1300 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2And the inclination when injecting the P-type material is 0-2 degrees.
Further, the N-type material is a group V element ion or a compound of group V element ions.
Further, when the N-type material is implanted into the P-type epitaxial layer twice in step 3, the energy of each implantation of the N-type material is sequentially increased, the dose of each implantation of the N-type material is sequentially decreased, and the inclination of each implantation of the N-type material is sequentially decreased.
Further, in the step 3, N-type material is implanted into the P-type epitaxial layer twice to form an N-type doped region, including:
for the first time: the energy of the implanted N-type material is 190 keV-250 keV, and the dose of the implanted N-type material is 1 x 1012cm-2～3.5×1013cm-2The inclination when injecting the N-type material is 3-7 degrees;
and (3) for the second time: the energy of the N-type material is 300 keV-700 keV, and the dosage of the N-type material is 1 x 1011cm-2～9×1012cm-2And the inclination when the N-type material is injected is 0-2 degrees.
The invention also provides a pixel unit, which comprises a P-type substrate and a P-type epitaxial layer arranged above the P-type substrate, and is characterized in that an N-type doped region and a P-well isolation region are arranged at the upper part of the P-type epitaxial layer, and a suspended diffusion node is arranged at the upper part of the P-well isolation region;
a transmission gate is arranged on the upper surface of the P-type epitaxial layer;
a P-type isolation region is arranged between the pixel unit and the adjacent pixel unit and/or the logic circuit region;
further, the P-well isolation region is formed by non-uniformly doping a P-type material.
Further, the depth of the P-well isolation region is not less than the depth of the photodiode.
Compared with the prior art, the invention has the beneficial technical effects that:
according to the invention, the heavily doped regions are formed between the pixel units and the logic circuit region to realize the isolation of the pixels and the adjacent region, the width of the isolation region can be well controlled by a mature mask technology, a narrower isolation region can be formed by adjusting the concentration of the doping material, the effect of inhibiting the body region crosstalk is well realized, the area waste between the pixel units and the logic circuit region is reduced, and the filling factor is effectively improved.
The isolation region is formed without etching and filling of an insulating medium, but a heavily doped region is formed by injecting a doping material to isolate crosstalk of charges, the existing ion injection equipment can be fully utilized, the method has good compatibility with the existing preparation process, the process is simplified, and the production cost is reduced.
Drawings
FIG. 1 is a schematic diagram of a pixel unit according to the present invention;
FIG. 2 is a schematic structural diagram of two adjacent pixel units according to the present invention;
the symbols in the figures are represented as: 1-a P-type substrate; 2-P type epitaxial layer; 3-pixel cell; 4-logic circuit area; 301-N type doped region; 302-a transfer gate; 303 — floating diffusion nodes; 304-an isolation region; 305-P-well isolation regions; 401 — NMOS; 402-PMOS; 403-N type doped region; 5 — adjacent pixel cell.
The details of the present invention are explained in further detail below with reference to the drawings and examples.
Detailed Description
The following embodiments of the present invention are provided, and it should be noted that the present invention is not limited to the following embodiments, and all equivalent changes based on the technical solutions of the present invention are within the protection scope of the present invention.
Example 1:
the embodiment provides a method for manufacturing a pixel unit, which includes the following steps:
in this embodiment, in order to prevent the isolation region from being fabricated to affect the shape of the N-type doped region of the photodiode, the embodiment employs three times of implantation to make the concentration of the P-type material uniform from top to bottom.
Wherein the P-type material is a group III element ion or a compound of the group III element ion, such as boron ion.
The method specifically comprises the following steps:
for the first time: the energy of the implanted P-type material is 150 keV-300 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2The inclination when injecting the P-type material is 0-2 degrees;
and (3) for the second time: the energy of the implanted P-type material is 500 keV-700 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2The inclination when injecting the P-type material is 0-2 degrees;
and thirdly: the energy of the implanted P-type material is 1000 keV-1300 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2And the inclination when injecting the P-type material is 0-2 degrees.
the N-type material is a group V element ion or a compound of group V element ions, such as arsenic ion and phosphorus ion.
In order to meet the depth requirement required for absorbing near infrared light, for the first time: the energy of the implanted N-type material is 190 keV-250 keV, and the dose of the implanted N-type material is 1 x 1012cm-2～3.5×1013cm-2The inclination when injecting the N-type material is 3-7 degrees; and (3) for the second time: the energy of the N-type material is 300 keV-700 keV, and the dosage of the N-type material is 1 x 1011cm-2～9×1012cm-2And the inclination when the N-type material is injected is 0-2 degrees.
When the N-type material is implanted for the second time, the inclination is reduced, ions are implanted into a deep part, and a deep junction is formed, so that near infrared light is absorbed, and the quantum efficiency is improved.
And 4, injecting an N-type material into the upper part of the P-type epitaxial layer to form a suspended diffusion node. In order to form a low potential, the floating diffusion node layer can rapidly absorb photo-generated electrons when the transmission gate is conducted, and the doping concentration of the floating diffusion node layer is higher than that of the N-type doping region so as to form a lower potential region.
When the isolation zone is generated by injecting the P-type material three times in step 1, preferably:
for the first time: the energy of the P-type material is 200keV, and the dose of the P-type material is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and (3) for the second time: the energy of P-type material implantation is 600keV, and the dose of P-type material implantation is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and thirdly: the energy for implanting P-type material is 1100keV, and the dose for implanting P-type material is 8 × 1011cm-2The inclination when injecting the P-type material is 0 °.
The embodiment adopts the modulation transfer function MTF as an evaluation index, where the MTF is the ability of the image sensor to convert the contrast of an imaged object into an image at a specific resolution, and the image is sharper as the MTF is higher. The increase of the depth of the body region of the N-type doped region can cause part of photogenerated carriers to enter adjacent pixels to generate crosstalk, so that the definition of an image is reduced, and the MTF value is reduced. To effectively improve the MTF, isolation between adjacent pixels is required.
With the preferably three-shot energy parameter in this embodiment, the modulation transfer function MTF is 0.5.
Comparative example 1:
this example differs from example 1 in that: in the step 1, an isolation area is generated by injecting the P-type material for one time; the energy of the P-type material is implanted into the substrate at 100keV, and the dose of the P-type material is implanted at 8 x 1011cm-2The inclination when injecting the P-type material is 0 degree; after the above one injection of P-type material, the MTF was 0.2.
The MTF value obtained by the method is low, because a large implantation energy is needed to reach a deep implantation depth during single implantation, implanted ions are concentrated at the bottom of an isolation region, effective doping cannot be formed in the middle and the upper part, the isolation function cannot be achieved, crosstalk is easily generated between pixel units, and therefore the MTF is low.
Comparative example 2:
this example differs from example 1 in that:
when the P-type material is injected for three times in the step 1 to generate the isolation area:
for the first time: the energy of the P-type material is 100keV, and the dose of the P-type material is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and (3) for the second time: the energy of P-type material implantation is 600keV, and the dose of P-type material implantation is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and thirdly: the energy for implanting P-type material is 1100keV, and the dose for implanting P-type material is 8 × 1011cm-2The inclination when injecting the P-type material is 0 °.
At this time, the modulation transfer function MTF was 0.41.
Comparative example 3:
this example differs from example 1 in that:
when the P-type material is injected for three times in the step 1 to generate the isolation area:
for the first time: the energy of the P-type material is 200keV, and the dose of the P-type material is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and (3) for the second time: the energy of P-type material implantation is 400keV, and the dose of P-type material implantation is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and thirdly: the energy for implanting P-type material is 1100keV, and the dose for implanting P-type material is 8 × 1011cm-2The inclination when injecting the P-type material is 0 °.
At this time, the modulation transfer function MTF was 0.46.
Comparative example 4:
this example differs from example 1 in that:
when the P-type material is injected for three times in the step 1 to generate the isolation area:
for the first time: the energy of the P-type material is 200keV, and the dose of the P-type material is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and (3) for the second time: the energy of P-type material implantation is 600keV, and the dose of P-type material implantation is 8X 1011cm-2The inclination when injecting the P-type material is 0 degree;
and thirdly: the energy of the implanted P-type material is 900keV, and the dose of the implanted P-type material is 8 x 1011cm-2The inclination when injecting the P-type material is 0 °.
At this time, the modulation transfer function MTF was 0.36.
Example 2:
the embodiment provides a pixel unit, as shown in fig. 1 and 2, including a P-type substrate 1 and a P-type epitaxial layer 2 disposed above the P-type substrate 1, an N-type doped region 301 and a P-well isolation region 305 are disposed on an upper portion of the P-type epitaxial layer 2, and a floating diffusion node 303 is disposed on an upper portion of the P-well isolation region 305;
a transmission gate 302 is arranged on the upper surface of the P-type epitaxial layer 2;
a P-type isolation region 304 is arranged between the pixel unit 3 and the adjacent pixel unit 5 and/or the logic circuit region 4;
the depth of the P-type isolation region 304 is not less than the depth of the N-type doped region 301.
In this embodiment, two ends of the transfer gate 302 partially overlap the N-type doped region 301 and the floating diffusion node 303, respectively, so that when the transfer gate 302 is turned on, i.e., when a sufficient voltage is applied to the transfer gate 302, the P-type region at the lower portion of the transfer gate 302 is inverted to form a channel region, and the N-type doped region 301 is communicated with the floating diffusion node 303 to form a conductive channel, thereby transferring photo-generated electrons in the N-type doped region 301 to the floating diffusion node 303 for storage.
In the embodiment, the P-type isolation region 304 is doped with a high-concentration P-type material to form a high-potential region, so as to block the leakage of photo-generated charges to the adjacent pixel unit 5 and the logic circuit region 4, wherein the logic circuit region 4 includes an NMOS401 and a PMOS402, the PMOS402 is an N-type heavily doped region, the potential is low, the photo-generated charges are attracted during the exposure integration period, and a leakage current is generated, and the high potential of the P-type isolation region 304 effectively blocks the leakage of the photo-generated charges to the logic circuit region. The minimum width of the P-type isolation region 304 is related to the doping concentration of the P-type material, and the higher the doping concentration, the smaller the width required to achieve effective isolation.
In particular, to prevent the occurrence of the inverse triangular shape of the N-type doped region of the photodiode, the P-type isolation region 305 is formed by non-uniformly doping P-type material, preferably by implantation with a light top-bottom implantation, and the depth of the isolation region is not less than the depth of the photodiode.
As the photodiode N-type doped region 301 body region becomes larger, the low potential of the floating diffusion node 303 also becomes the center of attraction for the photo-generated electrons, causing the photo-generated electrons to leak into the floating diffusion node 303 during integration. Preferably, the present invention is provided with a P-well isolation region 305, which is formed by doping a P-type material to form a high potential region, and which encloses the region other than the upper surface of the floating diffusion node 303, thereby preventing the entry of photo-generated electrons. The boundary of the P-well isolation region 305 on the side close to the photodiode is located between the half of the transfer gate 302 and the boundary of the floating diffusion node 303. The minimum distance from the boundary of the P-well isolation region 305 close to the photodiode side to the boundary of the floating diffusion node 303 is related to the doping concentration of the P-type material of the P-well isolation region 305, and the higher the doping concentration is, the smaller the value of the minimum distance is, and meanwhile, the minimum distance is also influenced by the junction depth and concentration of the photodiode N-type doping region 301.
Claims (8)
1. A preparation method of a pixel unit for near-infrared laser detection is characterized by comprising the following steps:
step 1, injecting a P-type material into the edge of a P-type epitaxial layer (2) surrounding a pixel unit to form an isolation region (304);
step 2, forming a polysilicon gate on the upper surface of the P-type epitaxial layer (2), and etching the polysilicon gate to obtain a transmission gate (302);
step 3, injecting N-type material into the P-type epitaxial layer (2) twice to form an N-type doped region (403);
step 4, injecting N-type material into the upper part of the P-type epitaxial layer (2) to form a suspended diffusion node (303); in the step 1, P-type material is injected into the P-type epitaxial layer (2) around the edge of the pixel unit to form an isolation region (304), and at least two times of injections with different energies are included;
the energy of injecting the P-type material every time is increased in sequence, the dosage of injecting the P-type material every time is the same, and the inclination of injecting the P-type material every time is the same;
in the step 3, when the N-type material is implanted into the P-type epitaxial layer (2) twice, the energy of the N-type material implanted each time is sequentially increased, the dose of the N-type material implanted each time is sequentially decreased, and the inclination of the N-type material implanted each time is sequentially decreased.
2. The method of claim 1, wherein the P-type material is a group III element ion or a compound of a group III element ion.
3. The method for manufacturing a pixel unit for near-infrared laser detection according to claim 1, wherein in the step 1, P-type material is implanted into the P-type epitaxial layer (2) four times around the edge of the pixel unit to form an isolation region (304);
when the P-type material is implanted for four times, the energy of the P-type material implanted every time is sequentially increased, the dose of the P-type material implanted every time is the same, and the inclination of the P-type material implanted every time is the same.
4. The method for preparing a pixel unit for near-infrared laser detection according to claim 1, wherein the step 1 of implanting P-type material into the P-type epitaxial layer (2) around the edge of the pixel unit to form an isolation region (304) comprises:
for the first time: the energy of the implanted P-type material is 150 keV-300 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2The inclination when injecting the P-type material is 0-2 degrees;
and (3) for the second time: the energy of the implanted P-type material is 500 keV-700 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2The inclination when injecting the P-type material is 0-2 degrees;
and thirdly: the energy of the implanted P-type material is 1000 keV-1300 keV, and the dose of the implanted P-type material is 5 x 1011cm-2～1.5×1012cm-2And the inclination when injecting the P-type material is 0-2 degrees.
5. The method of claim 1, wherein the N-type material is a group V element ion or a compound of group V element ions.
6. The method for preparing a pixel unit for near-infrared laser detection according to claim 1, wherein the step 3 of implanting N-type material in the P-type epitaxial layer (2) twice to form an N-type doped region (403) comprises:
for the first time: the energy of the implanted N-type material is 190 keV-250 keV, and the dose of the implanted N-type material is 1 x 1012cm-2～3.5×1013cm-2The inclination when injecting the N-type material is 3-7 degrees;
and (3) for the second time: the energy of the N-type material is 300 keV-700 keV, and the dosage of the N-type material is 1 x 1011cm-2～9×1012cm-2And the inclination when the N-type material is injected is 0-2 degrees.
7. The pixel unit prepared by the preparation method for the pixel unit for the near-infrared laser detection according to any one of claims 1 to 6, comprising a P-type substrate (1) and a P-type epitaxial layer (2) arranged above the P-type substrate (1), wherein an N-type doped region (301) and a P-well isolation region (305) are arranged on the upper portion of the P-type epitaxial layer (2), and a suspended diffusion node (303) is arranged on the upper portion of the P-well isolation region (305);
a transmission gate (302) is arranged on the upper surface of the P-type epitaxial layer (2);
a P-type isolation region (304) is arranged between the pixel unit (3) and the adjacent pixel unit (5) and/or logic circuit region (4);
the depth of the P-type isolation region (304) is not less than that of the N-type doped region (301).
8. The pixel cell of claim 7, wherein the P-well isolation region (305) is formed by non-uniformly doping a P-type material.
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| CN101292355A (en) * | 2005-08-26 | 2008-10-22 | 美光科技公司 | Implanted isolation region for imager pixels |
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