Microdefect identification method of molecular beam epitaxy tellurium-cadmium-mercury film

Abstract

The invention discloses a microdefect identification method for a molecular beam epitaxy tellurium-cadmium-mercury film. The method comprises the following steps: providing the molecular beam epitaxy tellurium-cadmium-mercury film; removing a surface oxide layer by chemical corrosion; corroding the thin film based on a defect-sensitive oxidizing corrosive agent to obtain defect distribution (corresponding to corrosion pit distribution) in the tellurium-cadmium-mercury thin film; cutting and thinning the corrosion pit area by using a focused ion beam; a defect atomic image arrangement structure in the corrosion pit is observed through a transmission electron microscope, and typical dislocation and stacking fault atomic arrangement structures are distinguished; a specific area is tested through an X-ray energy dispersion spectrometer, and element distribution states of different defect areas are identified. The method directly reflects the structure, distribution and origin of the microdefects in the molecular beam epitaxy tellurium-cadmium-mercury thin film, and has great application value in the aspects of inhibiting tellurium-cadmium-mercury defects, improving the quality of the molecular beam epitaxy tellurium-cadmium-mercury crystal and the like.

Description

Technical Field

[0001] The invention relates to the field of narrow-bandgap semiconductor film and infrared detector manufacturing, and in particular to a method for identifying microscopic defects of a molecular beam epitaxial mercury cadmium telluride film. Background Art

[0002] Mercury cadmium telluride is an important narrow bandgap semiconductor with a direct bandgap, whose bandgap width can be continuously adjusted from 1.4eV to a negative bandgap as the ratio of cadmium atoms to mercury atoms changes. Mercury cadmium telluride has excellent photoelectric response in the infrared band and is therefore often used in the field of high-sensitivity infrared detectors.

[0003] Molecular beam epitaxy is a typical method for preparing HgCdTe thin films. The substrate for molecular beam epitaxy HgCdTe can be lattice-matched CdZnTe or silicon, germanium, gallium arsenide, etc. with large mismatch. However, due to substrate defects or epitaxial process deviations, there are often a large number of defects in molecular beam HgCdTe thin films, which will affect the crystal quality of the film and severely limit its carrier lifetime and mobility, thereby causing performance degradation of the photodetector.

[0004] The distribution of micro defects in HgCdTe epitaxial films is discrete and difficult to find intuitively. The half-width of the double-crystal X-ray diffraction rocking curve is often used to macroscopically reflect the overall crystal quality of a certain area, but this is not conducive to further understanding of the defect formation mechanism, and it cannot directly provide feedback to further optimize the epitaxial process. Therefore, it is necessary to develop a method for accurately identifying micro defects in HgCdTe epitaxial films, and infer the process-related defect causes from the atomic-level arrangement structure of micro defects. Summary of the invention

[0005] The purpose of the present invention is to provide a method for accurately identifying microscopic defects in mercury cadmium telluride epitaxial films. The problem of difficulty in judging the quality degradation of HgCdTe thin film crystals has been solved, and it will help to further improve the quality of HgCdTe molecular beam epitaxy.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented by the following technical means: A method for identifying microscopic defects of a molecular beam epitaxial mercury cadmium telluride film comprises the following steps: Step 1: Providing MBE HgCdTe thin film A mercury cadmium telluride film is grown by molecular beam epitaxy on a

[211] crystalline cadmium telluride or gallium arsenide substrate, wherein the surface of the film is a mercury cadmium telluride passivation layer of 100nm-300nm thick; the beam source flux ratio used is mercury: tellurium: cadmium telluride = 200:1:0.6-0.4, the growth temperature is 178-188°C, and the growth time is 2-4 hours; Step 2: corroding the oxide layer and passivation layer on the surface of the mercury cadmium telluride film with an organic solvent, and rinsing and cleaning the corroded surface, and blowing it dry with nitrogen after rinsing; the corroded organic solvent is a mixed solution of bromine and methanol, wherein the volume ratio of bromine to methanol is 1:50-200, and the corrosion time is 5-10s; the rinsing and cleaning uses anhydrous methanol, acetone and ethanol for 3 minutes each, then rinses with ultrapure water for 5 minutes, and finally blows it dry with nitrogen; Step 3: etching the internal defects of the mercury cadmium telluride film by an oxidizing etchant to form corrosion pits; the oxidizing etchant is an aqueous solution of hydrochloric acid (concentration range 36-38%), nitric acid (concentration range 68-69%) and potassium dichromate, and the proportion of each component is 100mL: 10-15mL: 20-25mL: 8-10g; the mercury cadmium telluride film is corroded by the etchant for 3-5 minutes, and two types of corrosion pit shapes and distributions are clearly observed under an optical microscope; Step 4: Physically deposit tungsten and carbon protective layers on the corrosion pits by selectively cutting, digging out and thinning the corrosion pits with a focused ion beam, and the total thickness of the deposited protective layers is 1500-2000nm; use a gallium ion beam to selectively cut, dig out and thin the two types of corrosion pit areas, and the cross-sectional thickness of the corrosion pits after thinning is 40-80nm; Step 5: Observe the atomic image arrangement structure at the corrosion pit by transmission electron microscopy; use transmission electron microscopy to scan the cross-sectional depth and bottom area of ​​the corrosion pit, and the electron beam acceleration voltage is 200kV; the observed depth of the triangular corrosion pit is 800-1100nm, and the depth of the leaf-shaped corrosion pit is 200-500nm; the corresponding microscopic defect types of the two observed corrosion pits are dislocation and stacking fault respectively; Step 6: Determine the element ratio at the corrosion pit by using an X-ray energy dispersive spectrometer. Use the X-ray energy dispersive spectrometer to perform energy spectrum test on the corrosion pit area and quantitatively measure the atomic ratio of mercury, tellurium and cadmium elements.

[0007] Furthermore, the mercury cadmium telluride thin film passivation layer is a high-component mercury cadmium telluride passivation layer, and the cadmium element in the high-component passivation layer accounts for at least 80% of the total number of cations.

[0008] Furthermore, the atomic ratio of mercury:cadmium:tellurium at the triangular corrosion pit is 2:1:3.6, and the atomic ratio of mercury:cadmium:tellurium at the leaf-shaped corrosion pit is 2.7:1:4.

[0009] The present invention identifies the formation origins of macroscopic defects of thin films from a microscopic scale, accurately distinguishes two types of macroscopic corrosion pits originating from edge dislocations and stacking faults, and directly identifies the differences in atomic arrangement structures and element distributions corresponding to the two macroscopic defects.

[0010] Compared with the prior art, the molecular beam epitaxial mercury cadmium telluride film is characterized by the method of the present invention, which can accurately identify the defect location and defect type inside the film, and reveal the defect formation process of the film from the binding kinetic behavior of molecular atoms, thereby optimizing the molecular beam process of the mercury cadmium telluride film. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG1 is a schematic diagram of a defect of a mercury cadmium telluride film provided by the present invention after being corroded by an oxidizing corrosive agent; Figure 2 The surface electron micrograph of the mercury cadmium telluride film provided by the present invention after being etched by an oxidizing etchant; Figure 3 This is an electron micrograph of a cross section containing three corrosion pits after being cut and dug out by a focused ion beam in the present invention; Figure 4 It is a high-resolution transmission electron micrograph of the bottom of the triangular and leaf-shaped corrosion pits described in the present invention; Figure 5 It is the atomic ratio of cadmium, tellurium and mercury elements in the triangular and leaf-shaped corrosion pit areas described in the present invention. DETAILED DESCRIPTION

[0012] In order to clarify the purpose and technical advantages of the present invention, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only specific embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention. Example

[0013] This embodiment provides a method for accurately identifying microscopic defects in a mercury cadmium telluride molecular beam epitaxial film, comprising the following steps: 1) Provide molecular beam epitaxial mercury cadmium telluride thin film. The specific operation is to perform molecular beam epitaxy of mercury cadmium telluride thin film on a

[211] crystal orientation cadmium zinc telluride or gallium arsenide substrate, using a beam source flux ratio of mercury: tellurium: cadmium telluride = 200:1:0.6-0.4, the growth temperature is set to 178-188℃, and the growth time is controlled at 2-4 hours.

[0014] 2) Etch and clean the surface of the molecular beam epitaxial HgCdTe film. The specific operation is to place the molecular beam epitaxial HgCdTe film in a Teflon basket, immerse the basket and the HgCdTe film in a bromine-methanol mixed solution, rotate the Teflon basket at a constant speed, remove the basket from the bromine-methanol mixed solution after 3-5 seconds, and rinse it in methanol, acetone, and ethanol for 3 minutes in turn, then rinse it in ultrapure water for five minutes, and finally blow it dry with pure nitrogen.

[0015] 3) Chemical etching of the interior of the molecular beam epitaxial mercury cadmium telluride film. The specific operation is to place the Teflon basket loaded with the clean surface of the mercury cadmium telluride film in an oxidizing corrosive agent under nitrogen protection, the proportion of each component is 100mL of water: concentrated hydrochloric acid: concentrated nitric acid: potassium dichromate: 8-10g, and rotate the Teflon basket at a constant speed and immerse it completely in the corrosive solution, and fully corrode for 3-8 minutes. Different defect types have different sensitivities to the corrosive agent. Different defects will form corrosion pits of different structures after etching. Figure 1 Schematic diagram of defective corrosion of HgCdTe film; 1 is the HgCdTe film layer, 2 is the CdZnTe or GaAs substrate layer; under an optical microscope or scanning electron microscope, two types of corrosion pits are observed, namely triangular and leaf-shaped. Figure 2 This is an electron scanning micrograph of the film surface after corrosion.

[0016] 4) Use a focused ion beam to select, protect, cut, dig out, and thin the corrosion area. The specific operation is to find a suitable corrosion pit area in the scanning electron microscope of the focused ion beam system to select a rectangular area. The length and width of the selected area are 8 microns and 2 microns respectively. The selected area is physically deposited with a double layer of tungsten and carbon protection. The total thickness of the two films is 1500-2000nm. Next, a gallium ion beam is used to cut both sides of the long side of the area from the vertical direction. The cutting depth is controlled at 5-10 microns. The bottom and one side are cut from the horizontal direction until they are completely penetrated. The ion beam acceleration voltage is 30kV. Then, the metal platinum probe in the system is lowered to the sample protection layer and fixed by ion bombardment welding. Then, a gallium ion beam is used from the horizontal direction to cut off the last edge of the selected area connected to the film. The selected area is completely separated from the film. Then, the dug out sample is welded to the copper table and the connection part with the probe is cut off. Finally, a gallium ion beam is used from the vertical direction to thin the long sides one by one until the thickness of the sample reaches 40-80nm. Figure 3 This is an electron micrograph of the interface after focused ion beam cutting. Figures 1 and 2 correspond to the cross-sections of the triangular corrosion pit and the leaf-shaped corrosion pit, respectively.

[0017] 5) Use transmission electron microscopy and X-ray energy dispersive spectrometer to test the cross-sectional depth, atomic structure arrangement and element distribution differences of the corrosion pits. The specific operations include: observing the depth information of the two corrosion pits under a low-magnification transmission electron microscope. The depth of the typical triangular corrosion pit is 800-1100nm, and the depth of the leaf-shaped corrosion pit is 200-500nm; using high-resolution scanning imaging to observe the atomic arrangement structure at the bottom of the two corrosion pits. Figure 4(a) and (b) are transmission electron micrographs of the bottom of a triangular corrosion pit and a leaf-shaped corrosion pit, respectively. The microscopic defect corresponding to the triangular corrosion pit is a longitudinal stacking fault, and the microscopic defect corresponding to the leaf-shaped corrosion pit is a transverse edge dislocation. The characteristic X-rays of mercury, cadmium, and tellurium elements in the two corrosion pit regions were quantitatively tested using an X-ray energy dispersive spectrometer. Figure 5 is the element distribution ratio of the two corrosion pit areas. The atomic ratio of mercury:cadmium:tellurium in the triangular corrosion pit is 2:1:3.6, and the atomic ratio of mercury:cadmium:tellurium in the leaf-shaped corrosion pit is 2.7:1:4.

[0018] By characterizing the molecular beam epitaxial HgCdTe film in this embodiment, the defect locations and defect types inside the film can be directly identified, and the defect formation process inside the HgCdTe film can be directly revealed from the bonding process of molecular atoms, further providing guidance for the optimization of the molecular beam process of the HgCdTe film.

[0019] This embodiment is only an example to clearly illustrate the invention and is not a limitation of the implementation method. Those skilled in the art should understand that the scope of the present invention includes but is not limited to the above embodiment. Various changes made to the present invention in other forms without departing from the spirit or basic characteristics of the present invention are included in the protection scope of the present invention.

Claims

1. A method for identifying microscopic defects in a molecular beam epitaxial mercury cadmium telluride thin film, characterized in that: The following steps are involved: Step 1: Providing MBE HgCdTe thin film A mercury cadmium telluride film is grown by molecular beam epitaxy on a [211] crystalline cadmium telluride or gallium arsenide substrate, wherein the surface of the film is a mercury cadmium telluride passivation layer of 100nm-300nm thick; the beam source flux ratio used is mercury: tellurium: cadmium telluride = 200:1:0.6-0.4, the growth temperature is 178-188°C, and the growth time is 2-4 hours; Step 2: corroding the oxide layer and passivation layer on the surface of the mercury cadmium telluride film with an organic solvent, and rinsing and cleaning the corroded surface, and blowing it dry with nitrogen after rinsing; the corroded organic solvent is a mixed solution of bromine and methanol, wherein the volume ratio of liquid bromine to anhydrous methanol is 1:50-200, and the corrosion time is 5-10s; the rinsing and cleaning uses anhydrous methanol, acetone and ethanol for 3 minutes each, then rinses with ultrapure water for 5 minutes, and finally blows it dry with nitrogen; Step 3: etching the internal defects of the mercury cadmium telluride film by an oxidizing etchant to form corrosion pits; the oxidizing etchant is an aqueous solution of hydrochloric acid with a concentration of 36-38%, nitric acid with a concentration of 68-69%, and potassium dichromate, and the proportion of each component is 100mL: 10-15mL: 20-25mL: 8-10g; the mercury cadmium telluride film is corroded by using the etchant for 3-5 minutes, and two types of corrosion pit shapes and distributions are clearly observed under an optical microscope; Step 4: Physically deposit tungsten and carbon protective layers on the corrosion pits by selectively cutting, digging out and thinning the corrosion pits with a focused ion beam, and the total thickness of the deposited protective layers is 1500-2000nm; use a gallium ion beam to selectively cut, dig out and thin the two types of corrosion pit areas, and the cross-sectional thickness of the corrosion pits after thinning is 40-80nm; Step 5: Observe the atomic image arrangement structure at the corrosion pit by transmission electron microscopy; use transmission electron microscopy to scan the cross-sectional depth and bottom area of ​​the corrosion pit, and the electron beam acceleration voltage is 200kV; the observed depth of the triangular corrosion pit is 800-1100nm, and the depth of the leaf-shaped corrosion pit is 200-500nm; the corresponding microscopic defect types of the two observed corrosion pits are dislocation and stacking fault respectively; Step 6: Determine the element ratio at the corrosion pit by using an X-ray energy dispersive spectrometer. Use the X-ray energy dispersive spectrometer to perform energy spectrum test on the corrosion pit area and quantitatively measure the atomic ratio of mercury, tellurium and cadmium elements.

2. The micro defect identification method according to claim 1, characterized in that: The mercury cadmium telluride thin film passivation layer is a high-component mercury cadmium telluride passivation layer, and the cadmium element in the high-component passivation layer accounts for at least 80% of the total number of cations.

3. The micro defect identification method according to claim 1, characterized in that: The atomic ratio of mercury:cadmium:tellurium in the triangular corrosion pit is 2:1:3.6, and the atomic ratio of mercury:cadmium:tellurium in the leaf-shaped corrosion pit is 2.7:1:4.

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