Blue-green light enhanced silicon-based avalanche photodiode photosensitive chip structure
By optimizing the structure of silicon-based avalanche photodiode, especially the secondary epitaxial growth of the N-type epitaxial layer II, the problem of low response and quantum efficiency of traditional silicon APD to blue-green light is solved, and higher responsiveness and quantum efficiency are achieved.
Patent Information
- Application Number
- CN202421388584.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-18
- Publication Date
- 2025-07-04
- Estimated Expiration
- 2034-06-18
AI Technical Summary
Traditional silicon APD detectors have low responsiveness and quantum efficiency to the blue-green light band. The blue-green light penetrates light in silicon materials, resulting in large amounts of absorption before incident light is absorbed, limiting the responsiveness and quantum efficiency.
A blue-green light-enhanced silicon-based avalanche photodiode photosensitive chip with a bottom-up structure is adopted, including a back metal electrode, an N+ type high-doped substrate, an N-type epitaxial layer I, an N-type charge region, an N-type epitaxial layer II, a P+ type photosensitive region, an isolation ring, an anti-reflection layer and a front metal electrode. By optimizing the doping concentration and thickness of each layer, especially the secondary epitaxial growth of the N-type epitaxial layer II, it controls the light absorption and carrier collision ionization rate of the avalanche region.
It significantly improves the responsiveness and quantum efficiency of the avalanche photodiode, ensures that the blue-green light can be effectively penetrated and fully absorbed, and improves the triggering probability and response speed of the avalanche signal.
Smart Images
Figure CN223067444U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of photodetectors, and relates to a photosensitive chip structure of a silicon-based avalanche photodiode detector that can enhance the responsivity and quantum efficiency in the blue-green light band. Background Art
[0002] Underwater laser communication has excellent characteristics such as good directivity, strong data transmission ability, immunity to electromagnetic radiation / nuclear radiation, and difficulty in being intercepted by the enemy. Compared with traditional underwater radio communication and underwater acoustic communication, it can effectively solve the contradictions among communication rate, communication distance, and communication security, and can provide high-speed, stable, and secure data transmission for underwater equipment such as submarines, autonomous underwater vehicles, and sensors. Therefore, underwater laser communication has become one of the research and attention hotspots in the field of underwater wireless communication in recent years. Blue-green lasers with wavelengths of 450-550 nm have very little light attenuation in seawater. Under good water quality conditions, their maximum penetration distance can reach more than 600 meters, which is the main carrier window for underwater laser communication.
[0003] The photodetector is an important part of the receiving end of the underwater laser communication system, and its performance affects the sensitivity of the entire communication system. There are usually several types such as PIN-type photodiodes (positive-intrinsic-negative photodiodes, PIN-PD), avalanche photodiodes (APD), and photomultiplier tubes (PMT). Thanks to characteristics such as high sensitivity, no need for a high-voltage power supply, small volume, good modulation, and easy integration, silicon APD is one of the most commonly used photodetectors in current underwater laser communication systems.
[0004] However, silicon materials have a strong absorption effect on blue-green light. Generally speaking, the higher the light absorption rate, the smaller its transmission depth. Therefore, the penetration depth of blue-green light in silicon materials is very shallow, only about 0.8-1.2 μm. For traditional silicon APDs with a reach-through structure, when blue-green light irradiates the device, most of the incident light will be absorbed before entering the APD absorption layer, resulting in a significant reduction in the number of carriers that can enter the APD multiplication layer to participate in the avalanche effect, greatly limiting the responsivity and quantum efficiency of silicon APDs in the blue-green light band. Summary of the Utility Model
[0005] (I) Purpose of the Utility Model
[0006] The object of the present utility model is to provide a photosensitive chip structure of a blue / green light-enhanced silicon-based avalanche photodiode, which solves the problem of low responsivity and quantum efficiency of traditional punch-through silicon APD detectors for incident light in the blue / green light band by introducing a secondary silicon epitaxial layer and optimizing the structural parameters of the APD photosensitive region / absorption region / charge region / avalanche region.
[0007] (II) Technical solution
[0008] To solve the above technical problems, the present utility model provides a photosensitive chip structure of a blue / green light-enhanced silicon-based avalanche photodiode, which sequentially includes, from bottom to top: a back metal electrode, an N+-type highly doped substrate, an N-type epitaxial layer I, an N-type charge region, an N-type epitaxial layer II, a P+-type photosensitive region, an isolation ring, an antireflection layer, and a front metal electrode.
[0009] Among them, the back metal electrode is located on the back of the N+-type highly doped substrate, and the N-type epitaxial layer I is located on the front of the N+-type highly doped substrate.
[0010] Among them, the N-type charge region is a structure implanted into the N-type epitaxial layer I.
[0011] Among them, the N-type epitaxial layer II is a structure grown by secondary epitaxy after the implantation of the N-type charge region in the N-type epitaxial layer I.
[0012] Among them, both the P+-type photosensitive region and the isolation ring are structures implanted into the N-type epitaxial layer II, and the isolation ring is located on both sides of the P+-type photosensitive region.
[0013] Among them, both the antireflection layer and the front metal electrode are located on the surface of the N-type epitaxial layer II, and the antireflection layer is located above the P+-type photosensitive region, and the front metal electrode is located on the two side surfaces of the P+-type photosensitive region.
[0014] Among them, the doping concentration of the N+-type highly doped substrate is between 10 17 ~10 20 cm -3 ; the doping concentration of the N-type epitaxial layer I is between 10 13 ~10 15 cm -3 ; the doping concentration of the N-type charge region is between 10 14 ~10 16 cm -3 ;
[0015] Among them, the doping concentration of the N-type epitaxial layer II is between 10 12 ~10 14 cm -3 ; the doping concentration of the P+-type photosensitive region is between 10 17 ~1020 cm -3 between; the isolation ring is N-type doped with a doping concentration between 10 14 ~10 16 cm -3 between.
[0016] Wherein, the thickness of the N+-type highly doped substrate is 20 - 200 μm; the thickness of the N--type epitaxial layer I is 1.5 - 4 μm.
[0017] Wherein, the thickness of the N-type charge region is 0.5 - 1 μm; the thickness of the N--type epitaxial layer II is 1.5 - 2.5 μm; the thickness of the P+-type photosensitive region is 0.2 - 0.4 μm.
[0018] (III) Beneficial Effects
[0019] The photosensitive chip structure of the blue-green light enhanced silicon-based avalanche photodiode provided by the above technical solution forms a P+ / N- / N / N- / N+ structure from top to bottom. The highly doped P+ layer is the photosensitive region, and its thickness is controlled to be between the relatively thin 0.2 - 0.4 μm. On the one hand, it can ensure that the incident light in the blue-green band can smoothly penetrate this layer and enter the absorption region. On the other hand, it can also avoid the situation of unstable doping during preparation due to the too thin layer. The low-doped N--type epitaxial layer II is the light absorption region, which is prepared by the method of secondary epitaxy, so its thickness can be accurately controlled within the range of 1.5 - 2.5 μm (about twice the absorption length of blue-green light), so as to ensure that the photons entering the APD absorption layer are fully absorbed, effectively improving the quantum efficiency while maintaining a low time jitter. The N layer is the charge region, which mainly provides the avalanche high electric field for the avalanche region and at the same time ensures that the carriers can reach the saturated drift velocity in the light absorption region, effectively improving the response speed of the APD. The N--type epitaxial layer I is the avalanche region, which mainly plays the role of increasing the number of initial photo-generated carriers. In the photosensitive chip structure provided by the present invention, the carriers drifting into the avalanche region and forming the avalanche signal are electrons, and the impact ionization rate of electrons is much higher than that of holes, so the triggering probability of the avalanche signal can be significantly increased, thereby effectively improving the responsivity of the APD. Description of the Drawings
[0020] Figure 1 It is a schematic diagram of the photosensitive chip structure of the blue-green light enhanced silicon-based avalanche photodiode provided by the present invention.
[0021] In the figure: 1. Back metal electrode; 2. N+-type highly doped substrate; 3. N--type epitaxial layer I; 4. N-type charge region; 5. N--type epitaxial layer II; 6. P+-type photosensitive region; 7. Isolation ring; 8. Anti-reflection layer; 9. Front metal electrode. Detailed Embodiments
[0022] To make the objectives, content, and advantages of the present utility model clearer, the following further describes in detail the specific implementation manners of the present utility model with reference to the accompanying drawings and embodiments.
[0023] Referring to Figure 1 as shown, the photosensitive chip structure of the blue-green light enhanced silicon-based avalanche photodiode in this embodiment includes: a back metal electrode 1, an N+-type highly doped substrate 2, an N-type epitaxial layer 3, an N-type charge region 4, an N-type epitaxial layer 5, a P+-type photosensitive region 6, an isolation ring 7, an antireflection layer 8, and a front metal electrode 9.
[0024] The back of the N+-type highly doped substrate 2 is the back metal electrode 1, and the front is the N-type epitaxial layer 3.
[0025] The N-type charge region 4 is a structure implanted into the N-type epitaxial layer 3.
[0026] The N-type epitaxial layer 5 is located above the N-type epitaxial layer 3 and the N-type charge region 4.
[0027] The P+-type photosensitive region 6 and the isolation ring 7 are both structures implanted into the N-type epitaxial layer 5. Specifically, the isolation ring 7 is located on both sides of the P+-type photosensitive region 6.
[0028] The antireflection layer 8 and the front metal electrode 9 are both located on the surface of the N-type epitaxial layer 5. Specifically, the antireflection layer 8 is located above the P+-type photosensitive region 6, and the front metal electrode 9 is located on the two side surfaces of the P+-type photosensitive region 6.
[0029] The preparation process of this embodiment is as follows:
[0030] Epitaxial layer growth: Using a low-pressure silicon epitaxial system, an N-type epitaxial layer 3 with a thickness of 4 μm and a doping concentration of 5×10 18 cm -3 is epitaxially grown on the front of an N+-type highly doped substrate 2 with a thickness of 200 μm and a doping concentration of 3×10 14 cm -3 .
[0031] Charge region preparation: Using the thermal oxidation method in a dry oxygen atmosphere, an oxide layer with a thickness of 500 nm ± 50 nm is prepared on the N-type epitaxial layer 3. The implantation window is defined by photolithography + wet etching, and phosphorus ions are implanted from the front using an ion implantation device: dose 1×10 14 cm -2 、energy 60 keV. Subsequently, the residual photoresist and surface oxide layer on the surface of the N-type epitaxial layer 3 are removed, and then high-temperature annealing is carried out in a dry oxygen atmosphere: temperature 1150 °C, time 6 h, to form the N-type charge region 4.
[0032] Secondary epitaxial layer growth: Using a low-pressure silicon epitaxial system, an N-type epitaxial layer 5 with a thickness of 2 μm and a doping concentration of 2×10 13 cm -3 is epitaxially grown on the front side of the wafer.
[0033] Photosensitive area preparation: Using thermal oxidation in a dry oxygen atmosphere, an oxide layer with a thickness of 500 nm ± 50 nm is prepared on the N-type epitaxial layer 5. The implantation window is defined by photolithography + wet etching. Boron ions are implanted from the front side using an ion implantation device: dose 3×10 16 cm -2 , energy 40 keV. Subsequently, the residual photoresist and surface oxide layer on the surface of the N-type epitaxial layer 5 are removed. Then, through high-temperature annealing: dry oxygen atmosphere, temperature 1150 °C, time 0.5 h, a P+-type photosensitive area 6 is formed.
[0034] Isolation ring preparation: The implantation window is defined on the front side of the wafer by photolithography + wet etching. Subsequently, phosphorus ions are implanted from the front side: dose 1×10 14 , energy 40 keV. After removing the residual photoresist and surface oxide layer on the surface of the wafer, through high-temperature annealing: temperature 1150 °C, time 2 h, an isolation ring 7 is formed.
[0035] Anti-reflection layer preparation: Using a dielectric film deposition process, a SiN x layer with a thickness of 100 nm ± 10 nm is deposited on the front side of the wafer. After defining the etching window by photolithography, the SiN x layer not covered by the photoresist is removed using inductively coupled plasma etching. Subsequently, the remaining photoresist on the surface of the wafer is removed to complete the preparation of the anti-reflection layer 8.
[0036] Back / front electrode preparation: A 1 μm ± 0.5 μm Al film is deposited on the back side of the wafer through a metal film deposition process to complete the preparation of the back metal electrode 1. Then, a 1 μm ± 0.5 μm Al film is deposited on the front side of the wafer again through a metal film deposition process. After defining the corrosion window by photolithography, the Al film is etched using a phosphoric acid aqueous solution to remove the photoresist, completing the preparation of the front metal electrode 9. Subsequently, the front and back electrodes are alloyed at a temperature of 420 °C.
[0037] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.
Claims
1. A photosensitive chip structure of a blue-green light enhanced silicon-based avalanche photodiode, characterized in that, It includes, from bottom to top in sequence: a back metal electrode, an N+-type highly doped substrate, an N-type epitaxial layer I, an N-type charge region, an N-type epitaxial layer II, a P+-type photosensitive region, an isolation ring, an antireflection layer, and a front metal electrode; The back metal electrode is located on the back surface of the N+-type highly doped substrate, and the N-type epitaxial layer I is located on the front surface of the N+-type highly doped substrate; The N-type charge region is a structure implanted into the N-type epitaxial layer I; The N-type epitaxial layer II is a structure grown epitaxially for the second time after the N-type charge region is implanted into the N-type epitaxial layer I; Both the P+-type photosensitive region and the isolation ring are structures implanted into the N-type epitaxial layer II, and the isolation ring is located on both sides of the P+-type photosensitive region; Both the antireflection layer and the front metal electrode are located on the surface of the N-type epitaxial layer II, and the antireflection layer is located above the P+-type photosensitive region, and the front metal electrode is located on the two side surfaces of the P+-type photosensitive region; The thickness of the N+-type highly doped substrate is 20 - 200 μm; the thickness of the N-type epitaxial layer I is 1.5 - 4 μm; The thickness of the N-type charge region is 0.5 - 1 μm; the thickness of the N-type epitaxial layer II is 1.5 - 2.5 μm; the thickness of the P+-type photosensitive region is 0.2 - 0.4 μm.
2. The photosensitive chip structure of the blue-green light enhanced silicon-based avalanche photodiode according to claim 1, characterized in that, The doping concentration of the N+-type highly doped substrate is between 10 17 and 10 20 cm -3 ; the doping concentration of the N--type epitaxial layer I is between 10 13 and 10 15 cm -3 ; the doping concentration of the N-type charge region is between 10 14 and 10 16 cm -3 .
3. The photosensitive chip structure of the blue and green light enhanced silicon-based avalanche photodiode according to claim 2, characterized in that, The doping concentration of the N-type epitaxial layer II is between 10 12 and 10 14 cm -3 ; the doping concentration of the P+-type photosensitive region is between 10 17 and 10 20 cm -3 ; the isolation ring is N-type doped, and the doping concentration is between 10 14 and 10 16 cm -3 .