CN118738192A - A blue-green light enhanced silicon-based avalanche photodiode and a method for preparing the same - Google Patents

Abstract

The invention discloses a blue-green light enhanced silicon-based avalanche photodiode, which sequentially comprises the following components from bottom to top: the semiconductor device comprises a back metal electrode, an anti-reflection layer, a P+ type non-depletion layer, a n+ type epitaxial layer, a P type active region, an N+ type contact layer, a spacer ring, a permanent bonding adhesive layer, a bonding substrate, a through hole electrode and a front metal electrode. The invention can effectively improve the avalanche signal triggering probability of the APD, thereby improving the detection efficiency of the blue-green light wave band.

Description

A blue-green light enhanced silicon-based avalanche photodiode and a method for preparing the same

Technical Field

The invention belongs to the technical field of photoelectric detectors and relates to a blue-green light enhanced silicon-based avalanche photodiode and a preparation method thereof.

Background Art

With the continuous development of photoelectric detection technology and optical communication technology, the demand for the detection of weak light and even single photons has become more urgent. At present, the commonly used weak light detection devices are mainly: photomultiplier tube (PMT) and avalanche photodiode (APD). PMT can detect short wavelengths and amplify photocurrent by 106 times or more. However, its high voltage, large size, short service life, and sensitivity to magnetic fields limit its application range. APD is a semiconductor detector with low power consumption, high sensitivity, and high internal gain, and it does not have the above-mentioned disadvantages of PMT. Therefore, it has attracted widespread attention and research in the field of weak light detection.

Silicon is the most widely used semiconductor material with the most mature preparation process. For APD detectors, silicon material is still one of the best choices for its large-scale application. In addition, thanks to the high impact ionization rate ratio and low tunneling current of silicon materials, silicon-based APDs also have the advantages of high gain, low noise, and high stability. At present, silicon-based APDs are often used for weak light and single photon detection in the visible light band (0.3-0.8μm) and near-infrared band (0.8-1.1μm).

However, due to the inherent characteristics of silicon materials, it has a strong absorption effect on incident light in the blue-green band. The high absorption coefficient makes the penetration depth of blue-green light in silicon smaller, which can further lead to the fact that after the photons in the blue-green band are absorbed by the shallow surface layer of the APD, most of the photogenerated carriers quickly diffuse to the silicon surface and recombine at the interface state on the surface. This surface absorption and recombination effect allows only a few photogenerated carriers to enter the depletion region of the APD, greatly reducing the photoelectric conversion efficiency and detection sensitivity of the blue-green band. Therefore, an improved APD structure is needed to improve the detection efficiency of blue-green light and improve the performance of silicon-based APD detectors in the blue-green band.

Summary of the invention

(I) Purpose of the Invention

The purpose of the present invention is to provide a blue-green light enhanced silicon-based avalanche photodiode and a preparation method thereof, and to precisely control the electric field distribution and non-depletion layer thickness of the APD by optimizing the high-temperature doping and back thinning processes, thereby improving the detection performance of the APD in the blue-green light band and solving the problem of low photoelectric conversion efficiency and detection sensitivity of the silicon-based APD detector to incident light in the blue-green light band.

(II) Technical solution

In order to solve the above technical problems, the present invention provides a blue-green light enhanced silicon-based avalanche photodiode structure, which includes, from bottom to top, a back metal electrode, an anti-reflection layer, a P+ type non-depletion layer, a Π-type epitaxial layer, a P-type active region, an N+ type contact layer, an isolation ring, a permanent bonding glue layer, a bonding substrate, a through-hole electrode, and a front metal electrode.

Wherein, the back metal electrode and the anti-reflection layer are both located on the back side of the P+ type non-depletion layer.

Wherein, the Π-type epitaxial layer is located on the front side of the P+-type non-depletion layer.

Among them, the P-type active area, N+ type contact layer, and isolation ring are all structures injected into the Π-type epitaxial layer, the P-type active area is located below the N+ type contact layer, the N+ type contact layer is located on the surface of the Π-type epitaxial layer, and the isolation ring is located on both sides of the N+ type contact layer.

Wherein, the permanent bonding adhesive layer is located on the front side of the II-type epitaxial layer.

Wherein, the bonding substrate is located on the front side of the permanent bonding adhesive layer.

The through-hole electrodes penetrate the permanent bonding adhesive layer and the bonding substrate, are located on both sides of the N+ type contact layer, and are connected to the front metal electrodes.

Wherein, the front metal electrode is located on the front side of the bonding substrate.

Preferably, the doping concentration of the P+ type non-depletion layer is between 10 ¹⁷ and 10 ²⁰ cm ^-3 ; the doping concentration of the Π type epitaxial layer is between 10 ¹³ and 10 ¹⁵ cm ^-3 ; the doping concentration of the P type active region is between 10 ¹⁴ and 10 ¹⁶ cm ^-3 ; the doping concentration of the N+ type contact layer is between 10 ¹⁶ and 10 ¹⁹ cm ^-3 ; the isolation ring is P-type doped, and the doping concentration is between 10 ¹⁴ and 10 ¹⁶ cm ^-3 .

Preferably, the thickness of the P+ type non-depletion layer is 0.05-0.1 μm; the thickness of the Π-type epitaxial layer is 3-5 μm; the thickness of the P-type active region is 1-3 μm; and the thickness of the N+ type contact layer is 0.5-1 μm.

Preferably, the peak electric field point of the blue-green light enhanced silicon APD is distributed in the Π-type epitaxial layer at a position about 1 μm away from the back surface of the P+-type non-depletion layer.

The present invention also provides a method for preparing a blue-green light enhanced silicon-based avalanche photodiode, comprising the following steps:

The first step is to select a P+ type highly doped silicon substrate and form a Π-type epitaxial layer on its front side.

In the second step, an oxide layer is formed on the surface of the Π-type epitaxial layer, and then a photoresist is coated on the surface of the oxide layer. After photolithography, the oxide layer is etched, and boron ions are injected from the front side. After removing the photoresist and the residual surface oxide layer, a P-type active area and an isolation ring are formed by high-temperature push junction.

The third step is to coat photoresist on the front side of the wafer, define the injection window by photolithography, etch the oxide layer, inject phosphorus ions, remove the photoresist and the residual surface oxide layer, and form an N+ type contact layer after high-temperature junction.

The fourth step is to spin-coat permanent bonding glue on the front side of the wafer, and then permanently bond the bonding substrate after laser or mechanical hole opening to the wafer.

The fifth step is to remove the bonding glue in the through hole of the bonding substrate and at the bottom of the through hole by a dry etching process, and use liquid metal slurry to fully fill the through hole, and then solidify the liquid metal slurry by a low temperature process to form a through hole electrode.

The sixth step is to deposit a metal layer on the front side of the wafer to form a front metal electrode.

The seventh step is to thin and polish the back side of the wafer to thin the P+ type highly doped silicon substrate to a designed thickness and complete the preparation of the P+ type non-depletion layer.

The eighth step is to deposit a dielectric film passivation layer on the back of the above-mentioned wafer, remove the photoresist after photolithography and etching the dielectric film layer, and then deposit metal on the back of the above-mentioned wafer. After photolithography again, metal corrosion is performed to remove residual photoresist, complete the preparation of the anti-reflective layer and the back metal electrode, and finally perform electrode alloying.

(III) Beneficial effects

The blue-green light enhanced silicon-based avalanche photodiode and the preparation method thereof provided by the above technical solution have the following beneficial effects:

Since the absorption length of blue-green light in silicon is very small, only about 0.8 to 1.2 μm, the blue-green light enhanced silicon-based avalanche photodiode structure provided by the present invention greatly reduces the surface dead zone thickness (0.05 to 0.1 μm) on the incident light side, so as to effectively suppress the surface absorption composite effect of silicon APD on blue-green light, and ensures the realization of ultra-thin dead zone through a preparation method combining permanent bonding with back thinning and polishing, thereby avoiding the occurrence of warping, fragmentation, etc. that are prone to occur during the processing of ultra-thin silicon wafers.

Secondly, in the blue-green light enhanced silicon-based avalanche photodiode provided by the present invention, by regulating the APD electric field distribution, the peak electric field point appears on the side of the incident light at a position about 1 μm away from the APD surface, thereby effectively improving the collection efficiency of photogenerated carriers, ensuring that most photogenerated carriers can enter the avalanche region of the APD, and realizing the improvement of the photoelectric conversion efficiency and detection sensitivity in the blue-green light band.

In addition, for the electron-hole pairs generated by the absorption of incident photon energy in the absorption layer, the electrons will drift toward N-type silicon along the direction of the electric field, while the holes will drift toward P-type silicon. The blue-green light enhanced silicon-based avalanche photodiode provided by the present invention adopts P-type highly doped material as a substrate, and after epitaxy and multiple injection diffusion, an N+/P/Π/P+ structure is formed. After the incident light passes through the P+ type surface dead zone, it enters the Π-type epitaxial layer and is absorbed to generate electron-hole pairs. The carriers that drift to the avalanche zone and form avalanche signals are electrons, and the ionization coefficient of electrons is much greater than the ionization coefficient of holes, that is, the probability of electrons triggering avalanches is much greater than that of holes, so this structure can effectively improve the probability of avalanche signal triggering of APD, thereby improving the detection efficiency of the blue-green light band.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a blue-green light enhanced silicon-based avalanche photodiode provided by the present invention.

2a to 2h are schematic diagrams of the process of preparing the blue-green light enhanced silicon-based avalanche photodiode provided by the present invention.

DETAILED DESCRIPTION

In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

1 , the blue-green light enhanced silicon-based avalanche photodiode structure provided by the present invention includes: a back metal electrode 1, an anti-reflection layer 2, a P+ type non-depletion layer 3, a Π-type epitaxial layer 4, a P-type active region 5, an N+ type contact layer 6, an isolation ring 7, a permanent bonding adhesive layer 8, a bonding substrate 9, a through-hole electrode 10, and a front metal electrode 11.

The back side of the P+ type non-depletion layer 3 is the back metal electrode 1 and the anti-reflection layer 2, and the front side of the P+ type non-depletion layer 3 is the Π type epitaxial layer 4. The P type active region 5, the N+ type contact layer 6, and the isolation ring 7 are all structures injected into the Π type epitaxial layer 4. Specifically, the P type active region 5 is located below the N+ type contact layer 6, and the isolation ring 7 is located on both sides of the N+ type contact layer 6. The permanent bonding adhesive layer 8 is located between the Π type epitaxial layer 4 and the bonding substrate 9. The through hole electrode 10 runs through the permanent bonding adhesive layer 8 and the bonding substrate 9, and is located on both sides of the N+ type contact layer 6. The front metal electrode 11 is located on the front side of the bonding substrate 9 and is connected to the through hole electrode 10.

According to the method for preparing the blue-green light enhanced silicon-based avalanche photodiode provided by the present invention, a 4-inch P+ type highly doped silicon wafer is used as an epitaxial substrate material, and the silicon APD detector prepared thereby is used as an embodiment of the present invention.

The preparation method of this embodiment comprises the following steps:

In the first step, a Π-type epitaxial layer 4 with a thickness of 5 μm and a doping concentration of 2×10 ¹³ cm ^-3 is epitaxially grown on the front side of a P+-type highly doped silicon substrate with a thickness of 525 μm and a doping concentration of 6×10 ¹⁹ cm ^-3 using a low-pressure silicon epitaxial system, as shown in FIG. 2a .

In the second step, a 500nm±50nm thick oxide layer is formed on the surface of the Π-type epitaxial layer 4 by thermal oxidation in a dry oxygen atmosphere, and then an injection window is defined by photolithography + wet etching, and boron ions are injected from the front: the dose is 5×10 ¹⁴ cm ^-2 , the energy is 200keV, and the residual photoresist and oxide layer on the surface of the Π-type epitaxial layer 4 are removed, and then a high-temperature push-in is performed in a dry oxygen atmosphere: the temperature is 1150°C, and the time is 12h, to form a P-type active area 5 and an isolation ring 7, see Figure 2b.

In the third step, an implantation window is defined on the front side of the wafer by photolithography + wet etching, and phosphorus ions are implanted on the front side using an ion implantation device: a dose of 1×10 ¹⁶ cm ^-2 and an energy of 40 keV. Subsequently, the residual photoresist and oxide layer on the surface of the wafer are removed, and then high temperature annealing is performed: dry oxygen atmosphere, temperature 1150°C, time 2h to form an N+ type contact layer 6, see Figure 2c.

In the fourth step, a 120 μm thick sapphire glass is selected as the bonding substrate 9, and a through hole with a diameter of 2 μm is opened on the bonding substrate 9 by laser or mechanical drilling. Then, a permanent bonding adhesive is spin-coated on the front side of the wafer, and the bonding substrate 9 with the through hole is permanently bonded to the wafer to form a permanent bonding adhesive layer 8, see Figure 2d.

In the fifth step, an inductively coupled plasma etching system is used to remove the bonding glue in the through hole of the bonding substrate 9 and at the bottom of the through hole, and then silver paste is used to fully fill the through hole and make the silver paste form an ohmic contact with the N+ type contact layer 6. The silver paste is cured by a low temperature process to form a through-hole electrode 10, see Figure 2e.

Step 6: Deposit a 1 μm±0.5 μm Al film on the front side of the wafer by a metal film deposition process, and make the Al film form good electrical contact with the through-hole electrode 10, thereby completing the preparation of the front metal electrode 11, as shown in FIG. 2f.

In the seventh step, the back side of the wafer is thinned to thin the P+ type highly doped silicon substrate to about 20 μm, and then the back side of the wafer is polished with high precision to thin the P+ type highly doped silicon substrate to 0.1 μm, thus completing the preparation of the P+ type non-depletion layer 3, see Figure 2g.

In the eighth step, a 100nm±10nm SiO ₂ /SiN _x composite dielectric layer is deposited on the back of the wafer by a dielectric film deposition process, and then an etching window is defined by photolithography. After the composite dielectric layer not covered by the photoresist is removed by inductively coupled plasma etching, the residual photoresist on the wafer surface is removed to complete the preparation of the anti-reflection layer 2. Subsequently, a 1μm±0.5μm Al film is deposited on the back of the wafer by a metal film deposition process, and after the etching window is defined by photolithography, the Al film is etched by phosphoric acid aqueous solution, and the residual photoresist on the back of the wafer is removed to complete the preparation of the back metal electrode 1. Finally, the front and back electrodes are alloyed at a temperature of 420°C, as shown in Figure 2h.

It can be seen from the above technical solution that the present invention has the following significant features:

(1) The present invention proposes a silicon-based avalanche photodiode structure with an ultra-thin surface non-depletion layer and an electric field distribution with high photogenerated carrier collection efficiency, which effectively suppresses the surface absorption and recombination effect of silicon APD on blue-green light and solves the problem of low photoelectric conversion efficiency and detection sensitivity of traditional silicon-based avalanche detectors in the blue-green light band.

(2) The present invention proposes a process method that combines permanent bonding with back-side thinning and polishing, which solves the problems of warping and fragmentation that are prone to occur during the processing of ultra-thin silicon wafers, and realizes the preparation of an ultra-thin surface non-depletion layer of silicon APD.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (10)

1. A blue-green light enhanced silicon-based avalanche photodiode, characterized in that it includes, from bottom to top: a back metal electrode, an anti-reflection layer, a P+ type non-depletion layer, a Π-type epitaxial layer, a P-type active region, an N+ type contact layer, an isolation ring, a permanent bonding glue layer, a bonding substrate, a through-hole electrode, and a front metal electrode. 2. The blue-green light enhanced silicon-based avalanche photodiode according to claim 1 is characterized in that the back metal electrode and the anti-reflection layer are both located on the back of the P+ type non-depletion layer; and the Π-type epitaxial layer is located on the front of the P+ type non-depletion layer. 3. The blue-green light enhanced silicon-based avalanche photodiode as described in claim 2 is characterized in that the P-type active region, the N+ type contact layer, and the isolation ring are all structures implanted into the Π-type epitaxial layer, the P-type active region is located below the N+ type contact layer, the N+ type contact layer is located on the surface of the Π-type epitaxial layer, and the isolation ring is located on both sides of the N+ type contact layer. 4. The blue-green light enhanced silicon-based avalanche photodiode according to claim 3, characterized in that the permanent bonding glue layer is located on the front side of the II-type epitaxial layer. 5 . The blue-green light enhanced silicon-based avalanche photodiode according to claim 4 , wherein the bonding substrate is located on the front side of the permanent bonding adhesive layer. 6. The blue-green light enhanced silicon-based avalanche photodiode as described in claim 5 is characterized in that the through-hole electrode penetrates the permanent bonding glue layer and the bonding substrate, is located on both sides of the N+ type contact layer, and is connected to the front metal electrode. 7. The blue-green light enhanced silicon-based avalanche photodiode according to claim 6, characterized in that the front metal electrode is located on the front side of the bonding substrate. 8. The blue-green light enhanced silicon-based avalanche photodiode according to claim 7, characterized in that the doping concentration of the P+ type non-depletion layer is between 10 ¹⁷ and 10 ²⁰ cm ^-3 ; the doping concentration of the Π-type epitaxial layer is between 10 ¹³ and 10 ¹⁵ cm ^-3 ; the doping concentration of the P-type active region is between 10 ¹⁴ and 10 ¹⁶ cm ^-3 ; the doping concentration of the N+ type contact layer is between 10 ¹⁶ and 10 ¹⁹ cm ^-3 ; the isolation ring is P-type doped, and the doping concentration is between 10 ¹⁴ and 10 ¹⁶ cm ^-3 . 9. The blue-green light enhanced silicon-based avalanche photodiode according to claim 8 is characterized in that the thickness of the P+ type non-depletion layer is 0.05-0.1 μm; the thickness of the Π-type epitaxial layer is 3-5 μm; the thickness of the P-type active region is 1-3 μm; and the thickness of the N+ type contact layer is 0.5-1 μm. 10. A method for preparing a blue-green light enhanced silicon-based avalanche photodiode, characterized by comprising the following steps: The first step is to select a P+ type highly doped silicon substrate and form a Π type epitaxial layer on its front side; The second step is to form an oxide layer on the surface of the II-type epitaxial layer, then coat the surface of the oxide layer with photoresist, etch the oxide layer after photolithography, inject boron ions on the front side, remove the photoresist and the residual surface oxide layer, and form a P-type active area and an isolation ring by high-temperature push-junction; The third step is to coat the front side of the wafer with photoresist, define the injection window by photolithography, etch the oxide layer, inject phosphorus ions, remove the photoresist and the residual surface oxide layer, and form an N+ type contact layer after high temperature push-up. The fourth step is to spin-coat a permanent bonding adhesive on the front side of the wafer, and then permanently bond the bonding substrate after laser or mechanical hole opening to the wafer; Step 5: removing the bonding glue in the through hole of the bonding substrate and at the bottom of the through hole by dry etching process, and filling the through hole with liquid metal slurry, and then curing the liquid metal slurry by low temperature process to form a through hole electrode; Step 6: depositing a metal layer on the front side of the wafer to form a front metal electrode; Step 7: Thinning and polishing the back side of the wafer to thin the P+ type highly doped silicon substrate to a designed thickness, thereby completing the preparation of the P+ type non-depletion layer; The eighth step is to deposit a dielectric film passivation layer on the back of the above-mentioned wafer, remove the photoresist after photolithography and etching the dielectric film layer, and then deposit metal on the back of the above-mentioned wafer. After photolithography again, metal corrosion is performed to remove residual photoresist, complete the preparation of the anti-reflective layer and the back metal electrode, and finally perform electrode alloying.