Low-damage etching and gradient passivation methods for very long-wavelength type-2 superlattice infrared detectors

Abstract

This application provides a low-damage etching and gradient passivation method for very long-wavelength (VLS) type-II superlattice infrared detectors, belonging to the field of VLS detection. It solves the sidewall current problem encountered during mesa etching in VLS detectors. The method includes the following steps: preparation of a VLS type-II superlattice epitaxial structure; fabrication of a mask on the VLS type-II superlattice epitaxial structure as a sample for subsequent steps; ultra-low temperature, ultra-low bias mesa etching; in-situ multi-step surface repair: after mesa etching, the sample is transferred to an atomic layer deposition chamber within a vacuum interconnect system for multi-step, in-situ repair of the mesa sidewalls; deposition of a multi-layer gradient passivation structure using atomic layer deposition technology. This application integrates ultra-low bias etching and atomic layer deposition technologies through a vacuum interconnect system, combined with a gradient passivation layer specifically designed for narrow bandgap superlattices, significantly suppressing sidewall leakage and improving detector performance.

Description

Technical Field

[0001] This application relates to the field of very long wave infrared detection technology, and in particular to a low-damage etching and gradient passivation method for a very long wave type II superlattice infrared detector. Background Technology

[0002] Very long-wave infrared (VLWIR) type II superlattice detectors have important applications in deep space exploration and Earth remote sensing. However, as the response wavelength increases, the band gap of the superlattice material decreases sharply (typically <50 meV), leading to an exponential increase in the device's dark current. Mesa sidewall leakage is the main contributing factor to this dark current.

[0003] In current device fabrication methods, mesa etching can cause the following defects: 1. Sensitive to Etching Damage: Very long-wavelength superlattices are extremely sensitive to ion bombardment damage introduced by dry etching. Traditional ICP (Inductively Coupled Plasma) etching (bias voltage > 100W) leads to severe sidewall lattice distortion, forming deep-level defects in narrow bandgap materials, which become centers of generation-recombination current (GR current).

[0004] 2. Sidewall passivation failure: Traditional monolayer SiO2 or SiN x The passivation film exhibits significant lattice and thermal mismatches at the superlattice interface, resulting in a high interface state density. Furthermore, very long-wavelength devices require even greater mesa heights (>5 μm), making it difficult for a single-layer film to achieve complete sidewall coverage.

[0005] 3. Significant tunneling leakage: Under reverse bias, the band bending of the sidewalls of very long wave devices can easily induce interband tunneling and trap-assisted tunneling, which cannot be effectively suppressed by traditional thin-layer passivation. Summary of the Invention

[0006] To address the sidewall current problem in mesa etching of very long wave superlattice detectors, this application proposes a low-damage etching and gradient passivation method for very long wave type II superlattice infrared detectors. By integrating ultra-low bias etching and atomic layer deposition (ALD) technology through a vacuum interconnect system and combining it with a gradient passivation layer designed specifically for narrow bandgap superlattices, the sidewall leakage current is significantly suppressed, thereby improving detector performance.

[0007] The technical solution adopted in this application is: a low-damage etching and gradient passivation method for a very long-wavelength type-II superlattice infrared detector, comprising the following steps: Step 1: Preparation of very long wave type II superlattice epitaxial structure; Step 2: Fabricate a mask on a very long wavelength type II superlattice epitaxial structure as a sample for subsequent steps; Step 3: Ultra-low temperature, ultra-low bias mesa etching: The sample is transferred to the ICP etching chamber through a vacuum interconnect system for mesa etching; Step 4: In-situ multi-step surface repair: After the mesa etching is completed, the sample is transferred to the atomic layer deposition chamber in the vacuum interconnect system for multi-step, in-situ repair of the mesa sidewalls; Step 5: Deposit a multi-layer gradient passivation structure using atomic layer deposition (ALD). The multi-layer gradient passivation structure consists of an interface layer, a wide bandgap barrier layer, an electric field dispersion layer, and a protective layer, from bottom to top.

[0008] Furthermore, it also includes step 6: metallization and device integration.

[0009] Furthermore, the very long wave type II superlattice epitaxial structure consists of a bottom contact layer, an absorption layer, a top contact layer, and a capping layer epitaxially grown sequentially on a GaSb substrate and a GaSb buffer layer, wherein the bottom contact layer, the absorption layer, and the top contact layer are all made of InAs / InAsSb superlattice or InAs / GaSb superlattice materials.

[0010] Furthermore, in step 2, an electron beam evaporation deposition of a NiCr metal hard mask is used, and an etching pattern is formed by photolithography and wet etching.

[0011] Furthermore, the process parameters within the ICP etching chamber in step 3 are as follows: Etching gas: A mixed gas system of Cl2 / N2 / CH4 / H2 is used; ICP power: 200W~400W; Bias power: 30W~80W; Chamber pressure: 3 mTorr ~ 8 mTorr; Substrate temperature: -20℃ to 20℃; Etching depth: Etching to the middle of the bottom contact layer or into the GaSb buffer layer.

[0012] Furthermore, step 4, the in-situ multi-step surface repair, includes: Step 1: Chlorine residue removal, using remote hydrogen plasma to remove residual Cl from the sidewalls. - ion; Step 2: Nitriding and dangling bond treatment, NH3 plasma is introduced to form a nitride transition layer with a thickness of <1nm on the sidewall.

[0013] Furthermore, the interface layer in the multilayer gradient passivation structure uses AlN or Al2O3 material with a thickness of 1nm~3nm to achieve charge pinning and band shaping. The wide bandgap barrier layer is made of Al2O3 material with a thickness of 5nm~15nm, and is used to achieve tunneling barrier. The electric field dispersion layer is made of HfO2 or ZrO2 material with a thickness of 10nm~30nm, and is used to mitigate electric field spikes. The protective layer uses SiO2 or SiN x Materials with a thickness of 200nm~500nm are used to achieve mechanical and environmental protection.

[0014] Furthermore, in step 5, each layer of the multilayer gradient passivation structure is continuously deposited in the atomic layer deposition chamber without breaking the vacuum between layers, and the process temperature is 150℃~200℃.

[0015] Furthermore, the vacuum level of the vacuum interconnection system is <1×10⁻⁶. -7 Torr.

[0016] Furthermore, remote hydrogen plasma was used to remove residual Cl from the sidewalls. - During ionization, the H2 flow rate is 100 sccm~300 sccm, the power is 150 W~250 W, and the time is 60 s~180 s.

[0017] The advantages of this application over the prior art are as follows: 1. This application employs ultra-low bias etching + hydrogen plasma repair, which reduces the defect density of generated recombination current by approximately two orders of magnitude; 2. This application reduces the tunneling probability by using the AlN negative fixed charge depletion surface and the uniform electric field distribution of +HfO2; 3. This application employs gradient bandgap passivation layer interface optimization, reducing the interface state density to <1×102 11 cm -2 eV -1 This effectively reduces leakage current during tunneling. Attached Figure Description

[0018] The following description, in conjunction with the accompanying drawings, further illustrates this application: Figure 1 A flowchart illustrating the method provided in this application embodiment; Figure 2 A comparison of IV curves for conventional etching (2a) and the etching method of this application (2b) tested under a bias of 77K and -50mV. Figure 3 This is a comparison diagram of the interface state density of traditional monolayer SiO2 passivation and the four-layer gradient passivation of this application, tested using the Terman method (high-frequency CV characteristic method). Detailed Implementation

[0019] like Figures 1 to 3As shown, this application provides a low-damage etching and gradient passivation method for a very long-wavelength type-II superlattice infrared detector. This method connects the ICP etching chamber and the atomic layer deposition (ALD) chamber via a vacuum interconnect system, and combines ultra-low temperature and ultra-low bias etching processes with a gradient bandgap passivation layer design. The main steps of this method are as follows: Step 1: Preparation of Very Long Wavelength Type II Superlattice Epitaxial Structure: A GaSb substrate is provided, a GaSb buffer layer is epitaxially grown on the GaSb substrate, and then a very long-wavelength type-2 superlattice epitaxial structure is grown on the GaSb buffer layer using molecular beam epitaxy (MBE). The epitaxial structure includes: Bottom contact layer: Utilizing N-type InAs / InAsSb superlattice or InAs / GaSb superlattice materials, with a doping concentration of 1e18cm⁻¹. -3 ; Absorption layer: Intrinsic very long wavelength InAs / InAsSb superlattice or InAs / GaSb superlattice material is used, InAs layer thickness > 4nm, cutoff wavelength is designed to be 14μm~18μm, and number of periods > 400; Top contact layer: Utilizing P-type InAs / InAsSb superlattice or InAs / GaSb superlattice materials, with a doping concentration of 1e18cm⁻¹. -3 ; Capping layer: made of InAs or GaSb material, with a thickness of 5nm~20nm.

[0020] Step 2: Mask preparation: NiCr metal hard mask (thickness 50nm~150nm) is deposited by electron beam evaporation. The etching pattern is formed by photolithography and wet etching. The very long wave type II superlattice epitaxial structure processed in this step is used as the sample.

[0021] The NiCr selected in this application has a lower reaction rate and a higher selectivity in Cl2 / CH4 / H2-based etching atmospheres, making it particularly suitable for etching mesa surfaces of very long-wavelength devices with depths of 5μm to 8μm. This effectively avoids the loss of control over mesa morphology caused by mask degradation.

[0022] Step 3: Etching of the mesa at ultra-low temperature and ultra-low bias: The sample is passed through a vacuum interconnection system (vacuum degree <1×10⁻⁶). -7 Torr is transmitted to the ICP etching chamber.

[0023] Etching gas: A mixed gas system of Cl2 / N2 / CH4 / H2 is used. The addition of CH4 / H2 is used to form a protective layer on the polymer sidewalls, reducing damage to the sidewalls caused by physical bombardment.

[0024] Process parameters: ICP power: 200W~400W (to reduce plasma density); Bias power: 30W~80W (significantly lower than conventional processes, based on the principle of minimizing physical sputtering); Chamber pressure: 3 mTorr ~ 8 mTorr; Substrate temperature: -20℃~20℃ (Low-temperature etching can suppress surface atomic migration during the etching process and reduce sidewall roughness).

[0025] Etching depth: Etching to the middle of the bottom contact layer or into the GaSb buffer layer, with a depth of 5μm~8μm (the very long wave absorption layer is thicker, and the mesa height is increased accordingly).

[0026] Step 4: In-situ multi-step surface repair: After etching, the sample is transferred to the atomic layer deposition chamber within the vacuum interconnect system (without breaking the vacuum) for multi-step, in-situ repair of the mesa sidewalls, including: Step 1: Chlorine Residue Removal. Residual chlorine on the sidewalls is removed using remote hydrogen plasma (H2 flow rate 100-300 sccm, power 150-250 W, time 60-180 s). - ion.

[0027] Step 2: Nitriding and Dangling Bond Treatment. NH3 plasma is introduced to form an ultrathin (<1 nm) nitride transition layer on the sidewalls. This step not only saturates the dangling bonds but, more importantly, provides a chemically well-bonded substrate for the subsequently deposited AlN interface layer, enhancing the pinning effect of the negatively fixed charge.

[0028] Step 5: Deposition of gradient bandgap passivation layer: This application employs atomic layer deposition (ALD) technology to deposit a multi-layer gradient passivation structure. Targeting the narrow bandgap and easily bendable surface bandgap characteristics of type-II superlattice materials, a multi-layer gradient passivation structure with distinct functions is designed, as follows: The first layer (interface layer) is made of AlN or Al2O3 material, with a thickness of 1nm to 3nm. Its function is charge pinning and band shaping. By utilizing the high-density negative fixed charge at the interface between AlN and the superlattice, a depletion layer is formed on the sidewall of the narrow bandgap material, raising the electron barrier and suppressing sidewall leakage at its source. This is an essential characteristic that distinguishes it from traditional passivation layers (such as SiO2).

[0029] The second layer (wide bandgap barrier layer) is made of Al2O3 material with a thickness of 5nm~15nm. Its function is to block tunneling. It provides a high wide bandgap barrier to physically block electron tunneling. The Al2O3 grown using atomic layer deposition technology is dense and conformal, ensuring full coverage of the high aspect ratio mesa sidewalls.

[0030] The third layer (electric field dispersion layer) is made of HfO2 or ZrO2 material with a thickness of 10nm~30nm. Its function is to mitigate electric field spikes. High-k materials can redistribute the electric field at the edge of the mesa, avoiding interband tunneling caused by electric field concentration.

[0031] The fourth layer (protective layer) is made of SiO2 or SiN. x The material, with a thickness of 200nm~500nm, functions as mechanical and environmental protection. It provides mechanical protection, moisture barrier, and electrical insulation.

[0032] Deposition sequence: All passivation layers were deposited continuously within the ALD chamber without breaking the vacuum between layers. The process temperature was controlled between 150℃ and 200℃.

[0033] Step 6: Metallization and Device Integration Holes were created in the top and bottom contact layers of the mesa by photolithography, and Ti / Pt / Au multilayer electrodes were deposited by electron beam evaporation, followed by rapid thermal annealing to form ohmic contacts.

[0034] Table 1 below shows the differences between the technical solution of this application and conventional mesa etching methods, as well as the technical problems solved by these differences and the corresponding beneficial effects. This table clearly illustrates the advantages of the technical solution of this application.

[0035] Table 1. Advantages of this application: .

[0036] This application tested 100 at a temperature of 77K. 100μm 2 IV curves of a unit under two different etching process conditions, such as Figure 2 As shown, Figure 2 This indicates that the dark current density for conventional etching at -50mV is 3×10⁻⁶. -3 A / cm 2 The dark current density of the etching method in this application is 3×10⁻⁶. -5 A / cm 2 The etching method described in this application reduces the dark current density by about two orders of magnitude, reduces the generation-recombination current defect density by about two orders of magnitude, and improves the detection rate by more than four times.

[0037] This application tested the interface state density of traditional monolayer SiO2 passivation and the four-layer gradient passivation of this application, such as Figure 3 As shown, Figure 3 This indicates that, at 0V, using the Terman method (high-frequency CV characteristic method) to test the interface, the passivation state density of traditional monolayer SiO2 is 1×10⁻⁶. 12 cm -2 eV -1The density of states at the four-layer gradient passivation interface in this application is reduced to <1×10⁻⁶. 11 cm -2 eV -1 Compared to traditional single-layer SiO2 passivation, it reduces the efficiency by more than an order of magnitude.

[0038] This application solves the complex problem of sidewall leakage in very long wave devices by combining ultra-low temperature and ultra-low bias mesa etching, in-situ multi-step surface repair, and gradient passivation based on band shaping. It achieves a synergistic effect that surpasses the simple superposition of the effects of individual technologies.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A low-damage etching and gradient passivation method for a very long-wavelength type-2 superlattice infrared detector, characterized in that: Includes the following steps: Step 1: Preparation of very long wave type II superlattice epitaxial structure; Step 2: Fabricate a mask on a very long wavelength type II superlattice epitaxial structure as a sample for subsequent steps; Step 3: Ultra-low temperature, ultra-low bias mesa etching: The sample is transferred to the ICP etching chamber via a vacuum interconnect system for mesa etching. The process parameters in the ICP etching chamber in Step 3 are as follows: Etching gas: A mixed gas system of Cl2 / N2 / CH4 / H2 is used; ICP power: 200W~400W; Bias power: 30W~80W; Chamber pressure: 3 mTorr ~ 8 mTorr; Substrate temperature: -20℃ to 20℃; Etching depth: Etching to the middle of the bottom contact layer or into the GaSb buffer layer; Step 4: In-situ Multi-Step Surface Repair: After the mesa etching is completed, the sample is transferred to the atomic layer deposition chamber within the vacuum interconnect system for multi-step, in-situ repair of the mesa sidewalls, including: Step 1: Chlorine residue removal, using remote hydrogen plasma to remove residual Cl from the sidewalls. - ion; Step 2: Nitriding and dangling bond treatment, NH3 plasma is introduced to form a nitride transition layer with a thickness of <1nm on the sidewall; Step 5: Deposit a multi-layer gradient passivation structure using atomic layer deposition (ALD) technology. The multi-layer gradient passivation structure consists of an interface layer, a wide bandgap barrier layer, an electric field dispersion layer, and a protective layer, from bottom to top. The interface layer in the multilayer gradient passivation structure uses AlN or Al2O3 material with a thickness of 1nm~3nm to achieve charge pinning and band shaping. The wide bandgap barrier layer is made of Al2O3 material with a thickness of 5nm~15nm, and is used to achieve tunneling barrier. The electric field dispersion layer is made of HfO2 or ZrO2 material with a thickness of 10nm~30nm, and is used to mitigate electric field spikes. The protective layer uses SiO2 or SiN x Materials with a thickness of 200nm~500nm are used to achieve mechanical and environmental protection.

2. The low-damage etching and gradient passivation method for a very long-wavelength type-two superlattice infrared detector according to claim 1, characterized in that: It also includes step 6: metallization and device integration.

3. The low-damage etching and gradient passivation method for a very long-wavelength type-two superlattice infrared detector according to claim 1 or 2, characterized in that: The very long wavelength type II superlattice epitaxial structure consists of a bottom contact layer, an absorption layer, a top contact layer, and a capping layer epitaxially grown sequentially on a GaSb substrate and a GaSb buffer layer. The bottom contact layer, the absorption layer, and the top contact layer are all made of InAs / InAsSb superlattice or InAs / GaSb superlattice materials.

4. The low-damage etching and gradient passivation method for a very long-wavelength type-two superlattice infrared detector according to claim 2, characterized in that: In step 2, an electron beam evaporation deposition of a NiCr metal hard mask is used, and the etching pattern is formed by photolithography and wet etching.

5. The low-damage etching and gradient passivation method for a very long-wavelength type-two superlattice infrared detector according to claim 1, characterized in that: In step 5, each layer of the multilayer gradient passivation structure is continuously deposited in the atomic layer deposition chamber without breaking the vacuum between layers, and the process temperature is 150℃~200℃.

6. A low-damage etching and gradient passivation method for a very long-wavelength type-two superlattice infrared detector according to claim 4 or 5, characterized in that: Vacuum degree of vacuum interconnection system <1×10 -7 Torr.

7. The low-damage etching and gradient passivation method for a very long-wavelength type-two superlattice infrared detector according to claim 1, characterized in that: Removal of residual Cl from sidewalls using remote hydrogen plasma - During ionization, the H2 flow rate is 100 sccm~300 sccm, the power is 150 W~250 W, and the time is 60 s~180 s.

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