CN217588946U

CN217588946U - Photoelectric detection structure and photoelectric detector

Info

Publication number: CN217588946U
Application number: CN202221400389.5U
Authority: CN
Inventors: 汪一飞; 邹仁亭; 权锐
Original assignee: Wuhan Silicon Integrated Co Ltd
Current assignee: Wuhan Silicon Integrated Co Ltd
Priority date: 2021-06-18
Filing date: 2022-06-07
Publication date: 2022-10-14
Anticipated expiration: 2032-06-07

Abstract

The utility model provides a photoelectric detection structure, including the shading metal that photosensitive zone and its top set up, the region that shading metal surrounded is optical windowing promptly, and the total area of N trap accounts for below 60% of optical windowing in the optical windowing. Through utilizing photocurrent and N trap area decoupling zero relation between the two, adopt and compare in prior art in the N trap of less area, realized that parasitic capacitance, dark current and noise current in the photoelectric detection structure are showing and are reducing, have increased photoelectric detection's sensitivity and accuracy, the utility model discloses still further provide the photoelectric detector who adopts this photoelectric detection structure.

Description

Photoelectric detection structure and photoelectric detector

Technical Field

The utility model relates to a photoelectric detection technical field, concretely relates to photoelectric detection structure and photoelectric detector.

Background

The photoelectric detection technology is widely applied to various intelligent devices at present, for example, the screen brightness automatic adjustment function and the screen automatic off function of answering a call of a smart phone are both applied to the ambient light detection technology. In the prior art, in order to improve the quantum efficiency of photoelectric detection, an optical windowing area as large as possible is generally used, and a corresponding lens and a corresponding optical path are designed in cooperation with the optical windowing, so that photon flux as large as possible is guided into an optical windowing area of a photoelectric detector. Meanwhile, the area of a PN junction depletion region is increased by adopting the N well area as large as possible, the quantum efficiency of photoelectric conversion is improved, and the photocurrent as large as possible is realized, so that the sensitivity of photoelectric detection is improved. Therefore, the photodetector in the prior art usually fills the optical window to the maximum extent by the N-well in the photosensitive region.

However, as the area of the N-well increases, the contact area between the N-well and the silicon dioxide also increases, so that noise electrons generated by silicon dioxide interface state defects are more easily collected by the N-well to form dark current or noise current, and the dark current is more densely distributed in the whole N-well. The generation of dark and noise currents results in a decrease in the signal-to-noise ratio of the detection current in the photodetector. Meanwhile, the parasitic capacitance of the photoelectric tube is correspondingly increased due to the increase of the area of the N trap. In the field of low light detection such as ambient light sensors and proximity sensors, in order to obtain a larger photoelectric signal, an integrating circuit equivalent to the operational amplifier shown in fig. 1 is generally used to integrate the photocurrent generated by the photoelectric tube. According to the total noise calculation of the integrating circuit, the total noise output by the integrating circuit is positively correlated with the parasitic capacitance of the photoelectric tube. Therefore, the increase of the N-well area in the photo-transistor will cause the total noise of the integration circuit to become large, so that the design difficulty of the integration circuit is increased accordingly. How to reduce dark current, noise current and parasitic capacitance in the photoelectric tube on the premise that the intensity of the optical signal meets the detection requirement has important significance for improving the sensitivity and accuracy of photoelectric detection.

SUMMERY OF THE UTILITY MODEL

In view of this, in order to promote photoelectric detection's sensitivity and accuracy, the utility model provides a photoelectric detection structure and photoelectric detector of non-full filling formula. By utilizing the non-fully-filled N-well structure and reducing the contact area of the N-well and the silicon dioxide, under the condition of only reducing partial photocurrent, the parasitic capacitance and dark current of the photoelectric tube are obviously reduced, so that the signal-to-noise ratio of detection current in photoelectric detection is greatly improved, and the technical bias of using the N-well area as large as possible in the prior art is overcome by utilizing the decoupling relation between the N-well area and the photocurrent size.

The utility model discloses a following technical scheme solves above-mentioned problem: a photodetecting structure, comprising: the light-sensitive device comprises a P substrate, a light-sensitive layer and a light-emitting layer, wherein an N well formed by doping is arranged in the P substrate, and the P substrate and the N well form a light-sensitive region together; and a shading metal is arranged above the photosensitive area, an area surrounded by the shading metal is an optical windowing window when the shading metal is overlooked from the upper part, and the total area of the N trap in the optical windowing window accounts for less than 60% of the optical windowing window.

Preferably, the total area of the N-wells within the optical fenestrations accounts for less than 10% of the optical fenestrations.

Preferably, the total area of the N-wells within the optical fenestrations accounts for less than 1% of the optical fenestrations.

Preferably, the photosensitive region is covered by a silicon dioxide layer.

Preferably, the photoelectric conversion device further comprises a metal contact part, wherein the metal contact part is connected to the N well through a gap in the silicon dioxide layer so as to extract the photocurrent.

Preferably, three separated strip-shaped N wells are arranged in the optical window when viewed from the top of the light shielding metal.

Preferably, the optical window is provided with a plurality of circular N wells when viewed from above the light shielding metal.

Preferably, a plurality of N wells are arranged in the optical window in a top view from above the light shielding metal, and a distance between a center point of each N well and a center point of an adjacent N well is the same.

Preferably, the N-wells are 1N-wells in a whole shape in a plan view from above the light shielding metal, and the shape of the N-wells is a cross shape.

The utility model also provides a photoelectric detector, its characterized in that, its photosensitive zone adopts aforementioned photoelectric detection structure.

The utility model has the advantages that: by utilizing the decoupling relation between the photocurrent and the area of the N trap and adopting the N trap with smaller area compared with the prior art, the parasitic capacitance, the dark current and the noise current in the photoelectric detection structure can be obviously reduced, and the sensitivity and the accuracy of photoelectric detection are improved.

Drawings

FIG. 1 is an equivalent integrating circuit for integrating photocurrent in photodetection;

FIG. 2 is a cross-sectional view of a prior art photodetecting structure;

FIG. 3 is a schematic diagram of doping concentration of a conventional photodetection structure;

FIG. 4 is a graph of dark current distribution within a prior art photodetection structure;

FIG. 5 is a cross-sectional view of a photodetecting structure according to one embodiment;

FIG. 6 is a top view of a photodetecting structure according to an embodiment;

fig. 7 is a schematic doping concentration diagram of a photodetecting structure according to an embodiment;

FIG. 8 is a diagram illustrating a dark current distribution within a photodetecting structure according to an embodiment;

FIG. 9 is a graph showing the variation trend of photocurrent, parasitic capacitance and SNR coefficient with respect to the N-well area;

FIG. 10 is a top view of a photodetecting structure according to the second embodiment;

FIG. 11 is a top view of a photodetection structure according to the third embodiment;

fig. 12 is a top view of a photodetection structure according to the fourth embodiment.

Detailed Description

The present invention will be described in further detail with reference to examples, but the present invention is not limited thereto.

Fig. 2 is a cross-sectional view of a conventional photodetection structure, in which a P substrate 7 is doped with an N well 1,P, which forms a photosensitive region together with the N well, and a depletion region 2 is formed between the P substrate 7 and the N well 1, and an internal electric field 3 is present in the depletion region 2. A doping concentration diagram of the photo-tube structure is shown in fig. 3. The photosensitive area is covered with a silicon dioxide layer 6. The metal contact 4 is connected into the N-well 1 through a void in the silicon dioxide layer 6 to extract the photocurrent. A shading metal 5 is arranged above the photosensitive area, and an area surrounded by the shading metal 5 is an optical window when the shading metal 5 is overlooked from the upper part. In order to obtain as large a photocurrent as possible, the N-well 1 fills the entire optical window when viewed from above the light-shielding metal 5.

However, for the photodetection technology, the sources of the dark current noise of the PN junction in the photocell are mainly the bulk dark current and the surface dark current, and the bulk dark current is proportional to the surface area of the N-well 1. For the surface dark current, the magnitude is determined by the surface defect state of the silicon dioxide layer 6 and the contact area between the N-well 1 and the surface of the silicon dioxide layer 6. Fig. 4 shows a dark current distribution diagram in the above-described photodetection structure. Thus, where the process is deterministic, reducing the N-well surface area can be viewed as reducing the magnitude of dark current approximately proportionally. Meanwhile, the parasitic capacitance of the photoelectric detection structure is mainly formed by a depletion region capacitor C _T And diffusion capacitance C _D Both are also proportional to the surface area of the N-well 1. Therefore, in order to reduce the parasitic capacitance and the dark current of the photodetection structure, it may be considered to reduce the surface area of the N-well 1, that is, to reduce the contact area of the N-well 1 and the silicon dioxide layer 6.

In the embodiment of the present invention, a non-full-filling type photodetection structure is exemplarily shown, that is, as shown in fig. 5, compared with the existing photodetection structure shown in fig. 2, in which the N-well 1 is set to fill up the whole optical windowing region for increasing the photocurrent, the photodetection structure in the first embodiment adopts the non-full-filling type structure, that is, in the optical windowing region, the three separated N-wells 1 are used to replace the large-area N-well 1 of the integrated structure in fig. 1, thereby reducing the contact area between the N-well and the silicon dioxide layer. As shown in fig. 6, compared to the prior art in which the N-well fills the entire optical windowing region, the N-well in embodiment 1 is provided as three separate stripe-shaped N-wells 1, and the windowing region is not completely filled by the N-well in the top view, which belongs to a non-fully-filled structure. Fig. 7 is a schematic diagram illustrating the doping concentration of the photodetection structure according to the first embodiment. In fig. 8, a dark current distribution diagram in the photodetection structure in accordance with the first embodiment is shown, and compared with the dark current distribution diagram in fig. 4, the dark current existing at the contact surface is significantly reduced due to the reduced total contact area of the N-well and the silicon dioxide layer. Meanwhile, due to the reduction of the whole area of the N trap, the parasitic capacitance of the photoelectric tube is synchronously reduced.

The method comprises the steps of simulating photocurrent and parasitic capacitance by controlling the percentage of the total area of an N well and the area of an optical windowing, comparing the photocurrent and the parasitic capacitance with parameters of the N well when the optical windowing is filled up, calculating a photocurrent proportional relation and a parasitic capacitance proportional relation, setting a multiple of the photocurrent proportional relation and the parasitic capacitance proportional relation as a signal-to-noise ratio coefficient, and comparing the signal-to-noise ratio coefficient with the parameters of the N well when the optical windowing is filled up, so that the variation trend of the photocurrent, the parasitic capacitance and the signal-to-noise ratio coefficient along with the reduction of the area of the N well can be obtained, and the specific data are shown in the following table.

Fitting the parameters in the above table can obtain a trend graph of the change of the photocurrent, the parasitic capacitance and the signal-to-noise ratio coefficient along with the change of the percentage of the N-well area and the optical windowing area, as shown in fig. 9. As can be seen from the figure, as the N-well area decreases, the photocurrent does not significantly decrease, but the parasitic capacitance almost linearly decreases, so that the snr coefficient monotonically decreases as the ratio of the total N-well area to the optical window increases. For the photocurrent, since the photocurrent is mainly composed of three components, respectively, a photo-generated electron current in the P region, a photo-generated hole current in the N region, and a barrier region (depletion region) generated current. The barrier region is in a depletion state, so that the electric field in the barrier region can enable carriers to perform drift motion, and almost all photogenerated carriers generated in the barrier region can be collected, so that the carrier loss caused by the current generated in the barrier region can be ignored. The minority carrier current of the P region and the minority carrier current of the N region can cause different minority carrier lifetime and diffusion length due to different doping concentrations of different regions, so that photogenerated carrier loss is caused to different degrees. In the structure of the sensing region in the first embodiment, the integrated large-area N well of the sensing region in the prior art is divided into multiple small-area N wells, so that the resulting result is that the volume of the depletion region in the phototube is reduced, and therefore, more photogenerated carriers cannot reach hundred percent of collection efficiency, which causes the reduction of photocurrent. However, a portion of the minority carriers originally generated in the N region and lost to the N region now turn into minority carriers generated in the P region and lost to the P region. For a photodetector designed under a common standard CMOS process, the doping concentration of an N well is generally higher than that of a P substrate, the minority carrier lifetime of the N well is shorter, more photogenerated carriers are lost, the loss of the whole photogenerated electrons is reduced due to the reduction of the volume of the N well, and the factor can cause the increase of photocurrent. Due to the reduction of the surface area of the N well, the photocurrent variation caused by the two factors can be approximately offset, so that the photocurrent with little total variation can be obtained under the condition that the surface area of the N well is reduced. Therefore, the photocurrent and the N-well area are decoupled. By utilizing the decoupling relation and the linear correlation relation between the parasitic capacitance and the N-well area, the parasitic capacitance can be greatly reduced under the condition of not remarkably reducing the photocurrent, so that the signal-to-noise ratio coefficient is obviously improved. As can be seen from the list, when the total area of the N-wells accounts for 60% of the optical windowing, the signal-to-noise ratio is 2 times that when the N-wells fill the entire optical windowing; when the proportion of the total area of the N well in the optical windowing is 10%, the signal-to-noise ratio coefficient is improved by more than 14 times compared with the situation that the N well fills the whole optical windowing; when the total area of the N-well accounts for 1% of the optical windowing, the signal-to-noise ratio is improved by more than 70 times compared with the case where the N-well fills the entire optical windowing. Meanwhile, the relation between the dark current and the area of the N trap is considered, the N trap with smaller area can obviously reduce the dark current, the noise current and the parasitic capacitance in the photoelectric tube, and the sensitivity and the accuracy of photoelectric detection are improved. The photoelectric detection structure has the advantages that the performance is improved, and the photoelectric detection structure has an obvious effect when the total area of the N trap accounts for less than 60% of the optical windowing proportion. The variation trend of the signal-to-noise ratio coefficient in fig. 9 also shows that, compared with the case where the N-well fills the entire optical windowing, when the total area of the N-well accounts for less than 10% of the optical windowing, the signal-to-noise ratio coefficient is further improved by more than 14 times; when the proportion of the total area of the N-well in the optical windowing is below 1%, the signal-to-noise ratio coefficient is more remarkably increased by more than 70 times.

And simultaneously, the utility model discloses embodiment two is still provided. In the second embodiment, as shown in fig. 10, a top view of the photodetection structure with N wells is that, in the optical windowing region, 9N wells 1 are arranged in a 3 × 3 pattern, and each N well is circular in shape. The total area of the 9N-wells is also significantly reduced compared to filling the entire optical window. Further, the N-wells in the optically windowed regions can also be arranged as other numbers of separate circular N-wells or other shaped N-wells.

The third embodiment is shown in fig. 11. In this embodiment, there are multiple N wells in the optical windowing region, and in order to ensure that the photo-generated electrons are collected by the N wells more uniformly, the distance between the center point of each N well and the center point of the adjacent N well is the same, and is a fixed distance d. The total area of the plurality of N-wells in the optical windowing region is reduced by a greater amount than if the entire optical windowing region was filled.

In addition, the utility model provides a fourth embodiment, the plan view that sets up the N trap among the photodetection structure is shown in fig. 12, sets up 1 holistic N trap in the optics windowing region, and the shape of N trap is "ten" style of calligraphy, compares in current photodetection structure, and the total area of N trap only accounts for below 60% of optics windowing. Further, the 1N well in the optical windowing region may have other shapes, such as a circle or a quadrangle.

The embodiment of the present invention further provides a photo detector, wherein the photo sensing region adopts the photo detection structure as in the previous embodiment.

Although the present invention has been described herein with reference to the illustrated embodiments thereof, which are merely preferred embodiments of the present invention, it is to be understood that the present invention is not limited thereto, and that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.

Claims

1. A photodetecting structure, comprising: the light-sensitive device comprises a P substrate, a light-sensitive layer and a light-emitting layer, wherein an N well formed by doping is arranged in the P substrate, and the P substrate and the N well jointly form a light-sensitive area; and a shading metal is arranged above the photosensitive area, an area surrounded by the shading metal is an optical windowing window when the shading metal is overlooked from the upper part, and the total area of the N trap in the optical windowing window accounts for less than 60% of the optical windowing window.

2. The photodetecting structure according to claim 1, characterized in that the total area of N-wells within the optical fenestrations accounts for less than 10% of the optical fenestrations.

3. The photodetecting structure according to claim 1, characterized in that the total area of N-wells within the optical fenestrations accounts for less than 1% of the optical fenestrations.

4. The photodetecting structure according to claim 1, characterized in that the photosensitive region is covered with a silicon dioxide layer.

5. The photodetection structure according to claim 4, characterized in that it further comprises a metal contact connected to the N-well through a void in the silicon dioxide layer, thereby drawing out a photocurrent.

6. The photodetecting structure according to claim 1, characterized in that there are three separate stripe-shaped N-wells in the optical fenestration, viewed from above the light-shielding metal.

7. The photodetecting structure according to claim 1, characterized in that a plurality of circular N-wells are provided in the optical fenestration, as viewed from above the light-shielding metal.

8. The photodetecting structure according to claim 1, wherein a plurality of N-wells are formed in the optical window in a top view from above the light shielding metal, and a center point of each N-well is at the same distance from a center point of an adjacent N-well.

9. The photodetecting structure according to claim 1, wherein the N-well is provided as 1 entire N-well in a shape of a cross when viewed from above the light-shielding metal.

10. A photodetector characterised in that its light-sensitive area employs a photodetecting structure according to claims 1-9.