Infrared detecting chip of second type superlattice and antireflection film coating method

Abstract

The application discloses a kind of second-class superlattice infrared detection chip antireflection film coating methods, vacuum coating method is used to the surface of substrate piece is alternatively plated by zinc sulfide and magnesium fluoride Formed by three groups of six-layer composite film layer, after all coating procedures are completed, gradient heat aging treatment is carried out.The antireflection film obtained by the coating method provided by the application has high transmittance, high film stability, and large signal amplification on the detector.The coating method of the application uses only two kinds of coating materials, and the coating process is relatively simple, which can be widely used in the substrate part of the optoelectronic chip in the second-class superlattice infrared detector to achieve the back antireflection effect.

Description

Technical Field

[0001] This application relates to the field of micro-nano fabrication technology in semiconductor process technology, and more specifically, to a method for coating an antireflection film on a type II superlattice infrared detector chip. Background Technology

[0002] Infrared detector optoelectronic chips are electronic components capable of detecting infrared radiation and are widely used in security monitoring, drones, and other fields. To improve the sensitivity and performance of infrared detectors, back-facing antireflection coating technology is widely employed. Currently, mainstream antireflection coating processes include vacuum evaporation, ion plating, and sputtering. Vacuum evaporation is a commonly used process; its principle is to heat the antireflection coating material to a high temperature, causing it to evaporate and deposit on the substrate surface to form a thin film. Ion plating uses an ion beam to bombard the antireflection coating material, ionizing it and depositing it on the substrate surface. Sputtering uses high-energy ions to bombard the antireflection coating material, sputtering it and depositing it on the substrate surface. In terms of material selection, commonly used antireflection coating materials include zinc sulfide, zinc selenide, and magnesium fluoride. Among these, zinc sulfide film has excellent optical and mechanical properties and is a commonly used antireflection coating material.

[0003] Existing single-layer antireflection films have high reflectivity and cannot completely eliminate reflected light, affecting the detector's sensitivity and signal-to-noise ratio. While double-layer antireflection films can effectively reduce reflectivity, problems such as film peeling, oxidation, and contamination are prone to occur during the fabrication process, depending on the coating material selection, leading to unstable film quality. These issues affect the performance and stability of optoelectronic chips, specifically in the following aspects: 1. Sensitivity: The presence of reflected light interferes with the detector's signal, affecting its sensitivity and detection capability. 2. Signal-to-noise ratio: The presence of reflected light increases noise, reduces the signal-to-noise ratio, and affects the detector's accuracy and reliability. 3. Stability: Instability in film quality can cause changes in the optical properties of the antireflection film, affecting the long-term stability and reliability of the detector. Therefore, for optoelectronic chip applications, it is necessary to select antireflection film materials and processes with good stability and balanced optical and mechanical properties to improve the detector's performance and stability. Simultaneously, it is necessary to strengthen the quality control and testing of antireflection films to ensure their stability and reliability. Existing multilayer film antireflection technology usually requires the use of two or more materials combined with multiple processes for preparation, such as the preparation method mentioned in patent application CN 101861659 A. To complete the preparation of multilayer films, multiple processes such as vacuum evaporation, magnetron sputtering, chemical deposition and atomic layer deposition need to be combined to complete the preparation process. This has problems such as complex steps and long process. Using too many materials will lead to increased costs.

[0004] The corresponding wavelength range of the type-II superlattice infrared detector chip is 3.7-4.8 μm. Therefore, it is necessary to ensure that the antireflection coating can provide good transmittance and anti-reflection properties in the corresponding wavelength range to improve the key technical indicators such as sensitivity and stability of the mid-wave infrared detector chip. Therefore, there is an urgent need to provide a multilayer coating method for type-II superlattice infrared detector chips that is simple to operate, low in cost, and has high transmittance and high stability of the antireflection coating. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for coating an antireflection film on a type II superlattice infrared detector chip, comprising the following steps:

[0006] (1) A vacuum deposition method was used to deposit a film layer on a clean substrate surface in the form of a first layer of ZnS / 488nm, a second layer of MgF2 / 834nm, a third layer of ZnS / 231nm, a fourth layer of MgF2 / 184nm, a fifth layer of ZnS / 535nm, and a sixth layer of MgF2 / 810nm, to obtain three sets of six-layer composite films of ZnS / MgF2.

[0007] (2) After all the coating processes are completed, a gradient heat preservation and aging treatment is carried out: first, the temperature is lowered to 90°C and held for 15 minutes, then the temperature is lowered to 70°C and held for 15 minutes, then the temperature is lowered to 50°C and held for 15 minutes, and finally the temperature is naturally lowered to room temperature and stored in a vacuum environment for 4 hours.

[0008] Specifically, the growth rate of ZnS in step (1) is The growth rate of MgF2 is

[0009] After the first and second groups of ZnS / MgF2 films are grown, they are aged at 90°C for 15 minutes before the next film is deposited. The first group of ZnS / MgF2 films includes a first layer of ZnS and a second layer of MgF2. The second group of ZnS / MgF2 films includes a third layer of ZnS and a fourth layer of MgF2.

[0010] Before coating, the substrate in the coating cavity is heated and kept at 100°C for 15 minutes.

[0011] The coating chamber is evacuated to a vacuum level below 1.0E-4Pa to perform the coating process.

[0012] In step (2), the temperature is naturally cooled to room temperature under a high vacuum of not less than 2.5E-3Pa.

[0013] The beneficial effects of this invention include:

[0014] (1) The antireflective film obtained by the coating method of the present invention has high transmittance: the average transmittance in the infrared mid-wave band (3.7-4.8um) is as high as 99.85%.

[0015] (2) The signal amplification of the detector is large: the average signal amplification level of the photodetector chip made on GaSb substrate can reach 30% by coating and measuring with a special test system.

[0016] (3) The antireflective film obtained by the coating method of the present invention has high film stability: the multi-stage temperature gradient aging treatment releases the film stress, which can be more tightly bonded to the substrate and can cope with more complex and changeable environments in actual use.

[0017] (4) The coating method of the present invention is highly controllable: only two coating materials are used, and the coating process is relatively simple and does not require complicated processing, so as to achieve the best coating effect at the lowest cost. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view of a multilayer film structure obtained by using the antireflection coating method for a type II superlattice mid-wave infrared detector chip according to the present invention.

[0019] Figure 2 For comparison of the transmittance curves of the double-layer to six-layer antireflection membrane technology in Comparative Example 1;

[0020] Figure 3 This is a comparison of the responsivity of 30 Class II superlattice mid-wave infrared detector chips before and after coating in Example 1 of the present invention;

[0021] Figure 4 This is a process flow diagram of the antireflection coating method for the second type of superlattice infrared detector chip of the present invention;

[0022] In the figure, 1 is the substrate; 2 is the ZnS layer; and 3 is the MgF2 layer. Detailed Implementation

[0023] The present invention will be further described and illustrated below with reference to embodiments. However, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the present invention and the embodiments, all other inventions and embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0025] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0026] First, let's introduce and explain several terms used in this application:

[0027] Vacuum evaporation: Vacuum evaporation is a method of coating by vacuum evaporation. This method involves creating a vacuum chamber containing the substrate, achieving a gas pressure of 10... -2 Heating the coating material to a pressure below Pa causes its atoms or molecules to vaporize from the surface, forming a vapor stream that is incident on the substrate surface and condenses to form a solid film.

[0028] Aging: By controlling the environment of the membrane layer, the internal stress of the membrane layer can be reduced and the contact strength between the membrane layer and the substrate can be increased.

[0029] Example 1: Method for depositing multilayer antireflection coating on a type II superlattice infrared detector chip

[0030] according to Figure 4 The process flow shown in this embodiment, specifically the antireflective coating deposition method, includes the following steps:

[0031] (1) Prepare a clean GaSb substrate and place it into the prepared coating cavity;

[0032] (2) Heat the substrate in the cavity and keep it at 100°C for 15 minutes in the cavity environment;

[0033] (3) Select the pre-set program, wait for the cavity vacuum to be evacuated to below 1.0E-4Pa, and start the automatic coating program to perform film deposition, wherein the growth rate of ZnS is... The growth rate of MgF2 is A six-layer composite film of ZnS / MgF2 was obtained by depositing the following layers: first layer ZnS / 488nm, second layer MgF2 / 834nm, third layer ZnS / 231nm, fourth layer MgF2 / 184nm, fifth layer ZnS / 535nm, and sixth layer MgF2 / 810nm. Figure 1 (As shown); After the first and second groups of ZnS / MgF2 films are grown, they are kept at 90℃ for 15 minutes for aging before the next film is deposited.

[0034] (4) After all the coating processes are completed, perform gradient heat preservation and aging treatment: first, cool down to 90℃ and hold for 15 minutes, then cool down to 70℃ and hold for 15 minutes, then cool down to 50℃ and hold for 15 minutes, and finally allow it to cool down naturally to room temperature under a high vacuum of not less than 2.5E-3Pa and store it in a vacuum environment for 4 hours.

[0035] Using the deposition method of this embodiment, a total of 30 type-II superlattice mid-wave infrared detector chips were obtained. Before deposition, these 30 detector chips were encapsulated using a Dewar flask and then subjected to performance testing using a mid-wave measurement system. The response voltage Vs1 of the uncoated chip in the mid-wave band was measured. The response voltage Vs2 of the coated chip was then measured again. The results are as follows: Figure 3 As shown in the figure. The comparison reveals that the chip responsivity is significantly improved before and after coating. The response voltage range of 30 chips before coating is 0.234V-0.347V, and the response voltage range after coating is 0.325V-0.482V. The average increase in response voltage before and after coating is 0.103V, and the responsivity improvement can reach 25%-30%.

[0036] The 30 six-layer antireflection membranes prepared in this embodiment remained stable at 77K in the liquid nitrogen cyclic impact test. After 20 consecutive environmental tests, each lasting 15 minutes of liquid nitrogen impact, no membrane peeling or performance degradation was observed.

[0037] By comparing 30 sets of data in this embodiment, it can be concluded that the film has a specific structure and special light reflection-transmission properties. It can utilize the destructive interference of reflected light generated on the front and back surfaces of the film to enhance transmission. This ensures that the optical path difference is zero after the incident light is reflected from the two surfaces, thus eliminating light reflection between them and improving the overall light utilization rate of the device.

[0038] Comparative Example 1: Method for depositing a double-layer antireflection coating on a type II superlattice infrared detector chip

[0039] The specific preparation method is as follows:

[0040] (1) Prepare a clean GaSb substrate and place it into the prepared coating cavity;

[0041] (2) Heat the substrate in the cavity and keep it at 100°C for 15 minutes in the cavity environment;

[0042] (3) Select the pre-set program, wait for the cavity vacuum to be evacuated to below 1.0E-4Pa, and start the automatic coating program to perform film deposition, wherein the growth rate of ZnS is... The growth rate of MgF2 is A ZnS / MgF2 bilayer composite film was obtained by depositing a first layer of ZnS / 488nm and a second layer of MgF2 / 834nm.

[0043] (4) After the coating process is completed, a gradient heat preservation aging treatment is carried out. First, the temperature is lowered to 90°C and held for 15 minutes, then lowered to 70°C and held for 15 minutes, then lowered to 50°C and held for 15 minutes, and finally allowed to cool down naturally to room temperature under a high vacuum of not less than 2.5E-3Pa and stored in a vacuum environment for 4 hours.

[0044] One of the 30 six-layer antireflection films prepared in Example 1 was selected and measured using a Fourier transform infrared spectroscopy (FTIR) instrument. The sample was placed in the testing device, the testing wavelength range was set to 3.7-4.8 μm, and the instrument's optical path was adjusted so that the light beam could pass through the sample and be projected onto the detector to obtain the test data. The double-layer antireflection film prepared in this example (corresponding to...) was also tested. Figure 2 The ZnS / MgF2 in the sample and the optional six-layer antireflection membrane prepared in Example 1 (corresponding to...) Figure 2 The transmittance of the three-layer ZnS / MgF2 was measured, and the results are as follows: Figure 2 As shown.

[0045] according to Figure 2 It can be seen that, in the target wavelength band, the ZnS / MgF2 bilayer film structure achieves maximum transmittance at 4.1 μm, but significant attenuation occurs on both sides. However, the six-layer film structure of this invention maintains extremely high transmittance, exceeding 99.85%, in the target wavelength band of 3.7-4.8 μm, without any significant attenuation.

Claims

1. A method for coating an antireflection film on a type-II superlattice infrared detector chip, characterized in that, It includes the following steps: (1) A vacuum deposition method was used to deposit a film layer on a clean substrate in the form of a first layer of ZnS / 488nm, a second layer of MgF2 / 834nm, a third layer of ZnS / 231nm, a fourth layer of MgF2 / 184nm, a fifth layer of ZnS / 535nm, and a sixth layer of MgF2 / 810nm, to obtain a ZnS / MgF2 six-layer composite film. (2) After all the coating processes are completed, a gradient heat preservation and aging treatment is carried out: first, the temperature is lowered to 90°C and held for 15 minutes, then the temperature is lowered to 70°C and held for 15 minutes, then the temperature is lowered to 50°C and held for 15 minutes, and finally the temperature is naturally lowered to room temperature and stored in a vacuum environment for 4 hours. In step (1), the growth rate of ZnS is 15 Å / S and the growth rate of MgF2 is 10 Å / S. After the first and second groups of ZnS / MgF2 films are grown, they are aged at 90°C for 15 minutes before the next film is deposited. The first group of ZnS / MgF2 films includes a first layer of ZnS and a second layer of MgF2, and the second group of ZnS / MgF2 films includes a third layer of ZnS and a fourth layer of MgF2.

2. The antireflective coating method according to claim 1, characterized in that, Before coating, the substrate in the coating cavity is heated and kept at 100°C for 15 minutes.

3. The antireflective coating method according to claim 1, characterized in that, The coating chamber is evacuated to a vacuum level below 1.0E-4Pa to perform the coating process.

4. The antireflective coating method according to claim 1, characterized in that, In step (2), the temperature is naturally cooled to room temperature under a high vacuum of not less than 2.5E-3Pa.

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