Multi-hole type diffusion-based diode structure for improving photon detection efficiency of single-photon avalanche diode and preparation method of multi-hole type diffusion-based diode structure

Abstract

The invention provides a multi-hole type diffusion-based diode structure capable of improving the photon detection efficiency of a single-photon avalanche diode and a preparation method of the multi-hole type diffusion-based diode structure. The diode is a photodiode, and a PN junction of the diode is of a diffusion structure based on a planar junction. The diffusion structure is located on a cap layer of the single photon avalanche diode, a P-type doped region generated by two times of diffusion is arranged at the center of the upper portion of the cap layer, and a diffusion region distributed in a honeycomb shape is formed through constraint of a plurality of round hole type diffusion holes in the first time of diffusion. In the second diffusion, a single circular diffusion area is formed through a single circular diffusion hole. According to the invention, the curvature distribution of the junction surface of the diffusion junction in the large photosensitive surface is improved, the avalanche probability of the multiplication region in the photosensitive surface is improved, the probability of triggering the avalanche when photon-generated carriers generated in the InGaAs absorption layer transit to the InP multiplication layer is further improved, and the performance improvement of the photon detection efficiency is realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronics technology, and in particular to a diode structure based on porous diffusion and its fabrication method for improving the photon detection efficiency of single-photon avalanche diodes. Technical Background

[0002] Currently, InGaAs single-photon avalanche diodes (SPDs) responding to the near-infrared band have great application prospects in fields such as lidar detection, 3D imaging, and laser communication. SPDs utilize the principle of impact ionization to achieve photoelectric conversion from weak optical signals to macroscopic electrical signals. A photon strikes the photosensitive surface and is absorbed in the absorption region, generating an electron-hole pair. This hole is driven by an electric field to drift into the multiplication region and trigger an avalanche, outputting an avalanche pulse which is identified as an avalanche signal. The probability of this process occurring is the photon detection efficiency. However, when the device is not exposed to near-infrared light, the avalanche count triggered by carriers generated due to recombination and other factors is called the dark count. The key to improving the performance of SPDs lies in increasing the photon detection efficiency while reducing the dark count.

[0003] Currently, planar InGaAs / InP junctions based on double zinc diffusion have become the mainstream design for InGaAs single-photon avalanche diodes. The key to this structure lies in two-step zinc diffusion, consisting of a deep diffusion and a shallow diffusion. The diffusion depth is controlled by adjusting the diffusion time and temperature. Deep diffusion forms a small circular diffusion region through a smaller diffusion aperture, while shallow diffusion forms a larger circular diffusion region through a larger diffusion aperture concentric with the deep diffusion aperture. The deep diffusion region defines the photosensitive surface of the single-photon avalanche diode, and the InP material region of the cap layer under deep diffusion is defined as the multiplication region. Shallow diffusion is used to prevent edge breakdown of the device caused by the large curvature of the local diffusion junction morphology.

[0004] Theoretically, the larger the area of ​​the photosensitive surface, the larger the area of ​​the multiplication region, which in turn improves the photon detection efficiency.

[0005] While dark counts are improved simultaneously, current mature InGaAs / InP double-zinc diffusion designs cannot simultaneously increase the photosensitive surface area and photon detection efficiency. In fact, due to the increased dark count, the dead time duty cycle required for recovery increases, reducing the probability that the device is in a detectable state when photons arrive, thus lowering photon detection efficiency. The principle limiting further improvements in photon detection efficiency for large photosensitive surface devices is that in traditional double-zinc diffusion manufacturing processes, the junction surface at the pixel center is flat with low curvature. This results in a lower collisional ionization probability in the pixel center region compared to the more curvature regions at the outer ring edges. The actual effective light response region is concentrated in a ring-shaped area at the junction of deep and shallow diffusion.

[0006] Currently, there are two main approaches to improving the photon detection efficiency of single-photon avalanche diodes (SPDs). The first involves adding optical structures, such as microlenses, to enhance optical absorption. This approach significantly increases the manufacturing cost and places extremely high demands on the design of the optical structure. The second approach improves the design of the absorption layer by thickening it to increase photon detection efficiency. However, since recombination in the absorption layer is a major source of dark counts, this design, while improving photon detection efficiency, also significantly increases the dark count. Therefore, there is currently no satisfactory solution to the problem of low photon detection efficiency in large-area SPDs. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a diode structure based on a porous diffusion to improve the photon detection efficiency of single-photon avalanche diodes. This diode can achieve a significant improvement in the photon detection efficiency of single-photon avalanche diodes with large photosensitive surfaces.

[0008] The purpose of this invention is to effectively improve the junction curvature of the central region of a single-photon avalanche diode with a large photosensitive surface by designing a porous diffusion-based avalanche diode structure, thereby improving the collision ionization probability of the multiplication region in the central region of the pixel, increasing the photon detection efficiency of the single-photon avalanche diode, and optimizing the detection performance of the single-photon avalanche diode.

[0009] The objective of this discovery is achieved using the following technical solution:

[0010] A diode structure based on multi-hole diffusion to improve the photon detection efficiency of a single-photon avalanche diode includes a single-photon avalanche diode device structure. The diode is a photodiode, and the PN junction of the diode is a diffusion structure based on a planar junction. The diffusion structure is located in the cap layer of the single-photon avalanche diode, and a P-type doped region generated by two diffusions is disposed at the center of the upper part of the cap layer. The first diffusion forms a honeycomb diffusion region by being constrained by multiple circular diffusion holes, and the second diffusion forms a single circular diffusion region by a single circular diffusion hole.

[0011] Furthermore, the substrate of the diode is made of InP material, and the upper layers of the substrate are, in sequence, an InP buffer layer, an InGaAs absorber layer, an InGaAsP gradient layer, an InP charge layer, and an InP cap layer with P-type doped regions.

[0012] Furthermore, the depth of the first honeycomb diffusion region is greater than the depth of the second single circular diffusion region.

[0013] Furthermore, the size of the circle tangent to the outermost ring boundary of the first honeycomb diffusion region is defined as the size of the photosensitive surface of the photodiode. The second single circular diffusion region is a concentric circle of the aforementioned circle, and the radius of the single circular diffusion region is greater than the radius of the circle tangent to the outermost ring boundary of the honeycomb diffusion region.

[0014] A method for fabricating a porous diffusion-based diode structure to improve the photon detection efficiency of single-photon avalanche diodes:

[0015] The formation of P-type doped regions is as follows:

[0016] First, by growing a SiNx dielectric film on the cap layer, and by photolithography and etching, multiple closely spaced circular diffusion holes are opened on the dielectric film. These diffusion holes are located at the center of the pixel, and a honeycomb-shaped first honeycomb deep diffusion region is formed through thermal diffusion process, namely the P-type honeycomb deep diffusion region.

[0017] Then, based on the first deep diffusion, a SiNx dielectric film is grown on the cap layer surface, and a second diffusion hole is opened in the center of the pixel through photolithography and etching processes. The area of ​​the second circular diffusion hole is larger than that of the first honeycomb diffusion area. A second single circular shallow diffusion area, namely the P-type shallow diffusion area, is formed through thermal diffusion process.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. Compared with the existing traditional double zinc diffusion design process, the honeycomb diffusion structure of the present invention can effectively improve the spatial curvature of the junction region below the center of the photosensitive element, increase the collision ionization probability of the multiplication region below the center of the photosensitive element, and optimize the photon detection efficiency of the single-photon avalanche diode.

[0020] 2. Compared to the traditional double zinc diffusion design process, the honeycomb diffusion structure of the present invention can be achieved simply by changing the photomask pattern.

[0021] From the perspective of device diffusion junction design, this invention proposes a diode structure based on multi-hole diffusion, which increases the curvature of the junction surface in the central region of a large photosensitive single-photon avalanche diode pixel, thereby increasing the collision ionization probability in the central region of the pixel, effectively improving the photon detection efficiency of the single-photon avalanche diode, and promoting the development of near-infrared single-photon detection technology to a higher level. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view of the diode structure of the present invention;

[0023] Figure 2 This is the two-step diffusion layout of the diode chip of the present invention;

[0024] Figure 3 This is a comparison between the diode of the present invention and the improvement of the traditional double-diffusion structure.

[0025] In the picture:

[0026] 1-InP cap layer, 2-P type shallow diffusion region, 3-P type honeycomb deep diffusion region, 4-InP charge layer, 5-InGaAsP gradient layer, 6-InGaAs absorber layer, 7-InP buffer layer, 8-InP substrate. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the accompanying drawings of the present invention are all in a simplified form and use non-precise proportions, and are only used for convenience and clarity in illustrating the purpose of the embodiments of the present invention. It should also be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0028] like Figure 1 As shown, this invention provides a diode structure based on multi-hole diffusion to improve the photon detection efficiency of a single-photon avalanche diode, including a single-photon avalanche diode device structure. The diode is a photodiode, and its PN junction is a diffusion structure based on a planar junction. This diffusion structure is located in the cap layer of the single-photon avalanche diode. A P-type doped region generated by two diffusion processes is disposed at the center of the upper part of the cap layer. The first diffusion forms a honeycomb diffusion region constrained by multiple circular diffusion holes, and the second diffusion forms a single circular diffusion region through a single circular diffusion hole.

[0029] Specifically, the cross-sectional view of the diode structure is as follows: Figure 1 As shown, the diode structure includes an epitaxial structure and a cap diffusion structure.

[0030] Specifically, in this example, the substrate of the diode is InP material. In this embodiment, as... Figure 1 As shown, the epitaxial structure of this diode includes an N-type InP substrate 8. The upper layers of the InP substrate 8 are, in sequence, an InP buffer layer 7, an InGaAs absorption layer 6, an InGaAsP gradient layer 5, an InP charge layer 4, and an InP cap layer 1 with P-type doped regions. The multiplication layer of the single-photon avalanche diode is located in the InP cap layer 1.

[0031] The upper center of the InP cap layer 1 has a diffused cap layer structure formed using a diffusion process, specifically as follows: Figure 1 and Figure 2 As shown.

[0032] Specifically, there is a P-type doped region at the center of the upper part of the InP cap layer 1, which is generated by two diffusion processes.

[0033] Specifically, the formation of the cap layer diffusion structure is as follows:

[0034] First, by growing a SiNx dielectric film on the cap layer, and by photolithography and etching, multiple closely spaced circular diffusion holes are opened on the dielectric film. These diffusion holes are located at the center of the pixel. By adjusting the time and temperature, a honeycomb-shaped first honeycomb deep diffusion region is formed through a thermal diffusion process, namely the P-type honeycomb deep diffusion region 3.

[0035] Then, based on the first deep diffusion, a SiNx dielectric film is grown on the cap layer surface, and a second diffusion hole is opened in the center of the pixel through photolithography and etching processes. The area of ​​the second circular diffusion hole is larger than that of the first honeycomb diffusion area. By adjusting the time and temperature, a second single circular shallow diffusion area, namely the P-type shallow diffusion area 2, is formed through thermal diffusion process.

[0036] After two diffusion processes, a P-type doped region is formed, located at the center of the upper part of the cap layer, such as... Figure 2 As shown. In the above diffusion structure formation process, Zn element is used for diffusion; after the P-type doped region is formed, the PN junction is formed.

[0037] like Figure 1 and 2 As shown, the depth of the first P-type honeycomb deep diffusion region 3 is greater than that of the second P-type shallow diffusion region 2. The size of the circle tangent to the outermost ring boundary of the P-type honeycomb deep diffusion region 3 is defined as the size of the photosensitive surface of the photodiode. The P-type shallow diffusion region 2 is a concentric circle of the aforementioned circle, and the radius of the P-type shallow diffusion region 2 is greater than the radius of the circle tangent to the outermost ring boundary of the P-type honeycomb deep diffusion region 3.

[0038] This invention relates to an InGaAs single-photon avalanche diode chip based on a Separate Absorption, Gradient, Charge, and Multiplication (SAGCM) epitaxial structure. A two-step diffusion structure is designed on the InP cap layer. Specifically, the first step diffuses a honeycomb-shaped deep diffusion region through multiple circular apertures, and the second step diffuses a single circular shallow diffusion region. This diffusion structure effectively improves the spatial curvature of the pixel center junction region of the single-photon avalanche diode, increases the collisional ionization probability at the pixel center, and enhances the photon detection efficiency of the single-photon avalanche diode.

[0039] In one embodiment, the specific steps of InP cap layer 1 are as follows:

[0040] 1. Deposition of silicon nitride diffusion mask;

[0041] 2. Open the first diffusion window, the diffusion window is as follows: Figure 2 The P-type honeycomb deep diffusion region 3 is formed by diffusion through multiple circular holes;

[0042] 3. Closed-tube diffusion;

[0043] 4. Open a second diffusion window, the diffusion window is... Figure 2 The single circular P-type shallow diffusion region 2 is shown in Figure 2;

[0044] 5. Closed-tube diffusion.

[0045] In one embodiment, the designed device is a back-illuminated single-photon avalanche diode. When the device operates in Geiger mode, the diode is biased to a voltage above its breakdown voltage. A uniform surface light source illuminates the center of the photosensitive element on the back of the device. The radius of the outermost ring of the deep diffusion region is taken as the radius of the photosensitive surface of the pixel. The laser power is attenuated until the light intensity irradiated per unit area is the single-photon irradiation intensity. At this moment, the photon is absorbed by the absorption layer of the designed device structure, generating an electron-hole pair. The hole rapidly migrates to the multiplication region through a high electric field and undergoes collisional ionization. Under the processing of the quenching circuit, a macroscopic avalanche pulse electrical signal is generated, which is recorded as a photon event. The diode structure based on porous diffusion designed in this invention increases the spatial curvature at the porous diffusion junction within the pixel plane under the definition of deep diffusion, increases the probability of collisional ionization in the multiplication region within the pixel plane, improves the light response probability within the pixel plane, and improves the uniformity of the light response within the pixel.

[0046] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A diode structure based on porous diffusion to improve the photon detection efficiency of a single-photon avalanche diode, comprising a single-photon avalanche diode device structure, characterized in that: The diode is a photodiode, and the PN junction of the diode is a diffusion structure based on a planar junction. The diffusion structure is located in the cap layer of the single-photon avalanche diode. A P-type doped region generated by two diffusions is set at the center of the upper part of the cap layer. The first diffusion forms a honeycomb diffusion region through multiple circular diffusion holes, and the second diffusion forms a single circular diffusion region through a single circular diffusion hole.

2. The diode structure based on porous diffusion for improving the photon detection efficiency of a single-photon avalanche diode according to claim 1, characterized in that: The diode's substrate is made of InP material, and the upper layers of the substrate are, in sequence, an InP buffer layer, an InGaAs absorber layer, an InGaAsP gradient layer, an InP charge layer, and an InP cap layer with P-type doped regions.

3. The diode structure based on porous diffusion for improving the photon detection efficiency of a single-photon avalanche diode according to claim 2, characterized in that: The depth of the first honeycomb diffusion region is greater than the depth of the second single circular diffusion region.

4. The diode structure based on porous diffusion for improving the photon detection efficiency of a single-photon avalanche diode according to claim 3, characterized in that: The size of the circle tangent to the outermost ring boundary of the first honeycomb diffusion region is defined as the size of the photosensitive surface of the photodiode. The second single circular diffusion region is a concentric circle of the above circle, and the radius of the single circular diffusion region is larger than the radius of the circle tangent to the outermost ring boundary of the honeycomb diffusion region.

5. A method for fabricating a diode structure based on porous diffusion to improve the photon detection efficiency of a single-photon avalanche diode as described in any one of claims 1 to 4, characterized in that: The formation of P-type doped regions is as follows: First, by growing a SiNx dielectric film on the cap layer, and by photolithography and etching, multiple closely spaced circular diffusion holes are opened on the dielectric film. These diffusion holes are located at the center of the pixel, and a honeycomb-shaped first honeycomb deep diffusion region is formed through thermal diffusion process, namely the P-type honeycomb deep diffusion region. Then, based on the first deep diffusion, a SiNx dielectric film is grown on the cap layer surface, and a second diffusion hole is opened in the center of the pixel through photolithography and etching processes. The area of ​​the second circular diffusion hole is larger than that of the first honeycomb diffusion area. A second single circular shallow diffusion area, namely the P-type shallow diffusion area, is formed through thermal diffusion process.

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