A method for processing the inner surface of the cold screen of a medium-wave infrared focal plane detector

Abstract

A method for processing the inner surface of a medium-wave infrared focal plane detector cold shield relates to the field of infrared photoelectric detector manufacturing and specifically comprises the following steps: cleaning the machined surface of the detector cold shield and covering the portion of the cold shield surface that does not require blackening with aluminum foil; vapor-depositing an InSb film as a base layer onto the inner surface of the detector cold shield, increasing the partial pressure of Ar gas in a vacuum chamber during vapor deposition, and then covering the inner surface of the detector cold shield with the InSb film again to complete the preparation of the InSb film; preparing a ZnS film on the exterior of the InSb film by ion vapor deposition; after the ion vapor deposition is completed, filling the vacuum chamber with Ar gas, and performing high-temperature baking and annealing on the cold shield; the InSb polycrystalline film prepared by the present invention has a strong film / substrate bonding strength, i.e., adhesion, and is not easy to fall off, thereby achieving good surface coverage; and covering the surface of the InSb polycrystalline film with a layer of ZnS anti-reflection film by ion vapor deposition to ensure that the InSb film has a high absorptivity of incident medium-wave infrared light.

Description

Technical Field

[0001] The present invention relates to the field of infrared photoelectric detector manufacturing, in particular to a method for processing the inner surface of a cold screen of a medium-wave infrared focal plane detector. Background Art

[0002] As is known to all, in order to improve the detection and identification capability of the target, the infrared focal plane detector is usually provided with a built-in optical component cold screen in the detector, which has the following functions: first, to achieve the matching of the detector field of view with the optical field of view of the system; second, by connecting with the cold head of the refrigerator, the detector itself is in a low temperature state to limit the influence of background infrared radiation; third, to suppress stray radiation and improve the detector's detection capability of the target; the basic characteristics of the cold screen are: first, the heat load is small, and a thin-wall structure is usually adopted to save the power consumption of the refrigerator and reduce the startup time of the detector; second, the inner surface has a low reflectivity, which is an important aspect to ensure that the important indicator "crosstalk" of the focal plane detector meets the use requirements.

[0003] The method to ensure that the inner surface of the cold screen has a low reflectivity to the infrared incident radiation in the working band of the detector is to perform surface treatment on the cold screen. Common treatment methods include coating with black paint, anodizing blackening, chemical plating blackening, etc.; the surface blackening layer obtained by different processing techniques has different thickness, roughness, and adhesion firmness to the base, and in particular, the suppression of stray radiation is also different; in the previously applied patent, Chinese patent publication number CN111637977A, the invention name is an automatic blackening device and blackening method for the cold screen of an infrared detector, which discloses: fixing the rotator by a fixed bracket, and driving the product on the hanging rack to perform blackening treatment by the rotation of the rotator to improve the technical characteristics of the instability of the blackening process, and its blackening method is cathode ray tube. The electrophoretic blackening method is a method of depositing paint on the inner surface of the cold screen using electrodes. Its characteristics are that the blackened layer of the cold screen is smooth and flat, and the blackened layer is firmly bonded to the cold screen base. However, compared with other cold screen blackening methods, the suppression effect on the stray radiation of the detector is relatively low; Chinese patent publication number CN105486411B, the invention name is a method for forming an integrated cold screen for infrared detectors, which discloses: the cold screen matte fins are directly electroformed together with the cold screen body, avoiding secondary bonding, reducing the overall quality of the cold screen, and working more efficiently. The cold screen blackening method is also an electrophoretic method; there is also a method in the prior art that uses copper oxidation to blacken the inner cavity of the cold screen, and the main component of the blackening layer is CuO; the advantage of this process is that the implementation method is relatively easy, The specular reflectivity in the 3-5 micron band is 1-2%. The main issues are: 1. The blackening layer is unstable from batch to batch, and the blackening color consistency is prone to fluctuation; 2. The black oxide layer has poor adhesion to the substrate; 3. The oxide layer has low density and easily changes color when touched. Furthermore, the blackening layer tends to turn red after high-temperature degassing, and the degassing temperature must be maintained below 150°C. Therefore, finding a better surface treatment method to achieve low reflectivity of the cold shield's inner surface to incident light in the detector's operating band is of great application value. Summary of the Invention

[0004] In order to overcome the deficiencies in the background technology, the present invention discloses a method for processing the inner surface of a cold screen of a medium-wave infrared focal plane detector, thereby reducing the reflectivity of the inner surface of the cold screen to the medium-wave infrared band and improving the optical crosstalk suppression performance of the infrared focal plane detector.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] A method for processing the inner surface of a medium-wave infrared focal plane detector cold shield comprises the following steps:

[0007] S1. Clean the surface of the processed detector cold shield to remove surface contamination, and cover the part of the cold shield surface that does not need to be blackened with aluminum foil;

[0008] S2. Place the cold screen into the vacuum chamber of the ion plating system and fix it. High-purity InSb and high-purity Sb materials are placed in the evaporation boat of the ion plating system respectively. The amount ratio of InSb:Sb is (10-12):1.

[0009] S3, following the previous step, the background pressure in the ion plating system is pumped down to less than 1×10 -4 Pa, use a heater to heat the cold screen to release the adsorbed gas from its surface;

[0010] S4, passing high-purity argon gas into the vacuum chamber and using Ar ion bombardment for cleaning;

[0011] S5. Adjust the vacuum degree, turn on the evaporation power supply, heat the evaporation boat until the high-purity InSb is melted, and then heat it up until the high-purity Sb material is melted into the high-purity InSb. Adjust the heater to heat the cold shield components. Adjust the DC pulse bias and pulse duty cycle of the ion plating pulse ion source, and adjust the evaporation boat temperature. Deposit an InSb film as a base layer to cover the inner surface of the detector cold shield.

[0012] S6. Increase the partial pressure of Ar gas in the vacuum chamber during evaporation, and coat the inner surface of the detector cold shield with an InSb film again as an InSb infrared absorption layer, completing the InSb film preparation and stopping the InSb+Sb evaporation.

[0013] S7. Using ion evaporation to prepare a ZnS thin film on the outside of the InSb thin film, ensuring that the thickness of the prepared ZnS thin film meets the requirements of the thickness of a medium-wave infrared single-layer anti-reflection film;

[0014] S8. After the ion evaporation is completed, the vacuum chamber is filled with Ar gas, and the cold screen is baked at a high temperature and then annealed.

[0015] In the method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector, in step S2, the purity of InSb is 99.9999%, and the purity of Sb is 99.999%.

[0016] In the method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector, the heating temperature of the heater in step S3 is 190-210 degrees, and the heating time is 30-40 minutes.

[0017] The method for treating the inner surface of the cold screen of the medium-wave infrared focal plane detector is as follows: in step S4, after high-purity argon gas is introduced into the vacuum chamber, the vacuum degree is maintained at 1.0-3.0 Pa, the filament power supply is turned on, a DC pulse bias is applied to -500 V, and the pulse duty cycle is set to 100%, and Ar is performed. + The ion bombardment cleaning time is 15-30 minutes.

[0018] The method for processing the inner surface of the cold screen of the medium-wave infrared focal plane detector is as follows: in step S5, the vacuum degree is adjusted to 3×10 -2 Pa, the evaporation boat is heated to 530-540°C to melt InSb, and then heated to 630-640°C to melt Sb into InSb, and the heater is adjusted to heat the cold shield component to 130-150°C; the pulse duty cycle of the ion plating pulse ion source is set to 50%, the DC pulse bias is adjusted to -200V, and the temperature of the evaporation boat is adjusted to maintain an evaporation rate of 2-20 nm / s.

[0019] In the method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector, the thickness of the base layer in step S5 is 100-300 nm, and the thickness of the infrared absorption layer in step S6 is 5.0-8.0 μm.

[0020] In the method for treating the inner surface of the cold shield of the medium-wave infrared focal plane detector, in step S6, the partial pressure of the Ar gas during evaporation is increased to 0.5-1.5 Pa, and the DC pulse bias and pulse duty cycle in step S5 are maintained.

[0021] In the method for treating the inner surface of the cold shield of the medium-wave infrared focal plane detector, in step S7, the method for preparing the ZnS thin film by ion plating evaporation is as follows: placing the ZnS material in an evaporation boat and heating it to 1100-1300° C., maintaining the DC pulse bias and pulse duty cycle in step S5, and preparing a ZnS thin film with a thickness of 0.44 μm and a ZnS purity of 99.99%.

[0022] The method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector is as follows: in step S8, the vacuum chamber is filled with Ar gas to 1.1×10 5 Pa, and bake the cold screen at 300℃ for 60-70min.

[0023] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0024] 1. The method for treating the inner surface of the cold shield of a medium-wave infrared focal plane detector described in the present invention is an ion plating method that can achieve wrap-around plating. This solves the problem that the inner surface of the cold shield has a complex structure and cannot be fully covered by conventional vacuum thermal evaporation or vacuum sputtering methods. The prepared InSb polycrystalline thin film has a strong film / substrate bonding strength, i.e., adhesion, and the film layer is not easy to fall off, which can achieve good surface coverage.

[0025] 2. The method for processing the inner surface of the cold screen of the medium-wave infrared focal plane detector of the present invention is to firstly -2 The detector cold shield was covered with InSb thin film under Pa, which achieved the purpose of increasing the adhesion strength between the deposited film and the cold shield substrate.

[0026] 3. In the method for treating the inner surface of the cold shield of a medium-wave infrared focal plane detector described in the present invention, when preparing the InSb thin film by ion plating, the dosage ratio of InSb and Sb is (10-12):1. This solves the problem of In segregation during InSb evaporation causing the atomic percentages of In and Sb in the evaporated film to deviate from the chemical dosage ratio of 1:1.

[0027] 4. The method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector described in the present invention performs high-temperature annealing on the plated InSb polycrystalline film in an Ar atmosphere and protected by a covering ZnS film, thereby improving the crystallization quality of the InSb polycrystalline film and enhancing the absorption of medium-wave infrared incident light.

[0028] 5. The method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector described in the present invention is to cover the surface of the prepared InSb polycrystalline film with a layer of ZnS anti-reflection film by ion evaporation method, thereby ensuring that the InSb film has a high absorption rate for incident medium-wave infrared light. DETAILED DESCRIPTION

[0029] The present invention can be explained in detail by the following examples, the purpose of which is to disclose the present invention and to protect all technical improvements within the scope of the present invention.

[0030] Example 1

[0031] S1. Clean the surface of the processed detector cold shield to remove surface contamination, and cover the part of the cold shield surface that does not need to be blackened with aluminum foil;

[0032] S2. Place the cold screen into the vacuum chamber of the ion plating system and fix it. Place 99.9999% pure InSb and 99.999% pure Sb materials into the evaporation boat of the ion plating system respectively, with the amount ratio of InSb:Sb being 10:1.

[0033] S3, following the previous step, the background pressure in the ion plating system is pumped down to less than 1×10 -4 Pa, use a heater to heat the cold screen to remove the adsorbed gas from its surface; the heater heating temperature is 190 degrees and the heating time is 30 minutes;

[0034] S4. After high-purity argon is introduced into the vacuum chamber, the vacuum degree is maintained at 1.0 Pa, the filament power supply is turned on, a DC pulse bias is applied to -500 V, and the pulse duty cycle is set to 100%. + The ion bombardment cleaning time is 15 min;

[0035] S5, adjust the vacuum degree to 3×10 -2Pa, turn on the evaporation power supply, heat the evaporation boat to 530°C to melt the InSb, then heat it to 630°C to melt the high-purity Sb material into the high-purity InSb, adjust the heater to heat the cold shield component to 130°C; set the pulse duty cycle of the ion plating pulse ion source to 50%, adjust the DC pulse bias to -200V, adjust the evaporation boat temperature to maintain an evaporation rate of 10 nm / s, and deposit an InSb film as a base layer to cover the inner surface of the detector cold shield; the base layer thickness is 155nm;

[0036] S6, increase the partial pressure of Ar gas in the vacuum chamber during evaporation by 0.5 pa, maintain the DC pulse bias and pulse duty cycle in step S5, and then cover the inner surface of the detector cold screen with an InSb film as the InSb infrared absorption layer to complete the InSb film preparation and stop the InSb + Sb evaporation; the thickness of the infrared absorption layer is 6.0μm;

[0037] S7. Prepare a ZnS thin film on the outside of the InSb thin film by ion evaporation to ensure that the thickness of the prepared ZnS thin film meets the thickness requirement of the medium-wave infrared single-layer anti-reflection film; the method for preparing the ZnS thin film by ion plating evaporation is: place the ZnS material in an evaporation boat and heat it to 1100°C, maintain the DC pulse bias and pulse duty cycle in step S5, and prepare a ZnS thin film with a thickness of 0.44μm and a purity of 99.99%.

[0038] S8. After the ion evaporation is completed, the vacuum chamber is filled with Ar gas to 1.1×10 5 Pa, and the cold screen is baked at 300℃ and annealed for 60min.

[0039] Example 2

[0040] S1. Clean the surface of the processed detector cold shield to remove surface contamination, and cover the part of the cold shield surface that does not need to be blackened with aluminum foil;

[0041] S2. Place the cold screen in the vacuum chamber of the ion plating system and fix it. Place 99.9999% pure InSb and 99.999% pure Sb materials in the evaporation boat of the ion plating system respectively, with the amount ratio of InSb:Sb being 12:1.

[0042] S3, following the previous step, the background pressure in the ion plating system is pumped down to less than 1×10 -4 Pa, use a heater to heat the cold screen to remove the adsorbed gas from its surface; the heater heating temperature is 210 degrees and the heating time is 40 minutes;

[0043] S4. After high-purity argon is introduced into the vacuum chamber, the vacuum degree is maintained at 3.0 Pa, the filament power supply is turned on, a DC pulse bias is applied to -500 V, and the pulse duty cycle is set to 100%. + The ion bombardment cleaning time is 30 min;

[0044] S5, adjust the vacuum degree to 3×10 -2 Pa, turn on the evaporation power supply, heat the evaporation boat to 540°C to melt the InSb, then heat it to 640°C to melt the high-purity Sb material into the high-purity InSb, adjust the heater to heat the cold shield component to 150°C; set the pulse duty cycle of the ion plating pulse ion source to 50%, adjust the DC pulse bias to -200V, adjust the evaporation boat temperature to maintain an evaporation rate of 20 nm / s, and deposit an InSb film as a base layer to cover the inner surface of the detector cold shield; the base layer thickness is 300nm;

[0045] S6, increase the partial pressure of Ar gas in the vacuum chamber during evaporation to 1.5 pa, maintain the DC pulse bias and pulse duty cycle in step S5, and then cover the inner surface of the detector cold screen with an InSb film as the InSb infrared absorption layer to complete the InSb film preparation and stop the InSb + Sb evaporation; the thickness of the infrared absorption layer is 8.0μm;

[0046] S7. Prepare a ZnS thin film on the outside of the InSb thin film by ion evaporation to ensure that the thickness of the prepared ZnS thin film meets the thickness requirement of the medium-wave infrared single-layer anti-reflection film; the method for preparing the ZnS thin film by ion plating evaporation is: place the ZnS material in an evaporation boat and heat it to 1300°C, maintain the DC pulse bias and pulse duty cycle in step S5, and prepare a ZnS thin film with a thickness of 0.44μm and a purity of 99.99%.

[0047] S8. After the ion evaporation is completed, the vacuum chamber is filled with Ar gas to 1.1×10 5 Pa, and the cold screen is baked at 300℃ and annealed for 70min.

[0048] The parts not described in detail in this invention are prior art.

[0049] The embodiments selected herein for the purpose of disclosing the invention are presently considered suitable, but it should be understood that the invention is intended to include all variations and modifications of the embodiments that fall within the scope of the concept and invention.

Claims

1. A method for processing the inner surface of a medium-wave infrared focal plane detector cold shield, characterized by: The specific steps include the following: S1. Clean the surface of the processed detector cold shield to remove surface contamination, and cover the part of the cold shield surface that does not need to be blackened with aluminum foil; S2. Place the cold screen into the vacuum chamber of the ion plating system and fix it. High-purity InSb and high-purity Sb materials are placed in the evaporation boat of the ion plating system respectively. The amount ratio of InSb:Sb is (10-12):

1. S3, following the previous step, the background pressure in the ion plating system is pumped down to less than 1×10 -4 Pa, use a heater to heat the cold screen to release the adsorbed gas from its surface; S4, passing high-purity argon gas into the vacuum chamber and using Ar ion bombardment for cleaning; S5, adjust the vacuum degree to 3×10 -2 Pa, turn on the evaporation power supply, heat the evaporation boat until the high-purity InSb is melted, and then heat it up until the high-purity Sb material is melted into the high-purity InSb. Adjust the heater to heat the cold shield components. Adjust the DC pulse bias and pulse duty cycle of the ion plating pulse ion source, and adjust the evaporation boat temperature. Evaporate the InSb film as a base layer to cover the inner surface of the detector cold shield. S6. Increase the partial pressure of Ar gas in the vacuum chamber during evaporation, and coat the inner surface of the detector cold shield with an InSb film again as an InSb infrared absorption layer, completing the InSb film preparation and stopping the InSb+Sb evaporation. S7. Using ion evaporation to prepare a ZnS thin film on the outside of the InSb thin film, ensuring that the thickness of the prepared ZnS thin film meets the requirements of the thickness of a medium-wave infrared single-layer anti-reflection film; S8. After the ion evaporation is completed, the vacuum chamber is filled with Ar gas, and the cold screen is baked at a high temperature and then annealed.

2. The method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector according to claim 1, characterized in that: In step S2, the purity of InSb is 99.9999%, and the purity of Sb is 99.999%.

3. The method for processing the inner surface of the cold shield of a medium-wave infrared focal plane detector according to claim 1, characterized in that: In step S3, the heating temperature of the heater is 190-210 degrees, and the heating time is 30-40 minutes.

4. The method for processing the inner surface of the cold shield of a medium-wave infrared focal plane detector according to claim 1, characterized in that: In step S4, high-purity argon gas is introduced into the vacuum chamber, and the vacuum degree is maintained at 1.0-3.0 Pa. The filament power supply is turned on, a DC pulse bias is applied to -500 V, and the pulse duty cycle is set to 100%. + The ion bombardment cleaning time is 15-30 minutes.

5. The method for processing the inner surface of the cold shield of a medium-wave infrared focal plane detector according to claim 1, characterized in that: In step S5, the evaporation boat is heated to 530-540°C to melt InSb, and then heated to 630-640°C to melt Sb into InSb. The heater is adjusted to heat the cold shield component to 130-150°C. The pulse duty cycle of the ion plating pulse ion source is set to 50%, the DC pulse bias is adjusted to -200V, and the temperature of the evaporation boat is adjusted to maintain an evaporation rate of 2-20 nm / s.

6. The method for processing the inner surface of the cold shield of a medium-wave infrared focal plane detector according to claim 1, characterized in that: The thickness of the primer layer in step S5 is 100-300 nm, and the thickness of the infrared absorption layer in step S6 is 5.0-8.0 μm.

7. The method for processing the inner surface of the cold shield of a medium-wave infrared focal plane detector according to claim 1, characterized in that: In step S6, the partial pressure of the Ar gas during evaporation is increased to 0.5-1.5 Pa, and the DC pulse bias and pulse duty cycle in step S5 are maintained.

8. The method for processing the inner surface of the cold shield of a medium-wave infrared focal plane detector according to claim 1, characterized in that: In step S7, the method for preparing the ZnS thin film by ion plating evaporation is as follows: the ZnS material is placed in an evaporation boat and heated to 1100-1300°C, while maintaining the DC pulse bias and pulse duty cycle in step S5, and the prepared ZnS thin film has a thickness of 0.44μm and a purity of 99.99%.

9. The method for processing the inner surface of the cold shield of the medium-wave infrared focal plane detector according to claim 1, characterized in that: In S8, the vacuum chamber is filled with Ar gas to 1.1×10 5 Pa, and bake the cold screen at 300℃ for 60-70min.