Molecular beam epitaxy device for reducing background doping and use method thereof

Abstract

The invention relates to the technical field of molecular beam epitaxy, and discloses a molecular beam epitaxy device capable of reducing background doping and a use method thereof.The molecular beam epitaxy device comprises an epitaxy chamber cavity internally provided with an active furnace and a substrate table, molecular beams evaporated by the source furnace comprise effective beams emitted to the substrate table and ineffective beams not passing through the substrate table, and the effective beams are different from the ineffective beams. The device further comprises a low-temperature pipe, the two ends of the low-temperature pipe are exposed out of the epitaxial chamber cavity, and the part, in the epitaxial chamber cavity, of the low-temperature pipe is coiled and wound to form a bent pipe for shielding invalid beams. In the molecular beam epitaxy device provided by the invention, the spirally wound low-temperature pipe is hermetically arranged in the epitaxy chamber cavity, so that during epitaxy, the background impurity concentration in the device can be effectively reduced, the pollution is reduced, the vacuum degree in the epitaxy chamber cavity is stabilized, and the efficiency of the device is improved. The epitaxial quality is improved; and the epitaxial chamber cavity is convenient to clean.

Description

Technical Field

[0001] The present application relates to the technical field of molecular beam epitaxy, and mainly to a molecular beam epitaxy device for reducing background doping and a method for using the same. Background Art

[0002] In thin film epitaxial growth technology, thin films obtained by molecular beam epitaxy (MBE) have attracted widespread attention due to their excellent interface quality and the advantages of low background impurity concentration doping. In order to obtain higher quality films, it is necessary to continue to improve the cleanliness of the epitaxial environment to reduce the possibility of interaction with unnecessary background gases during film growth, thereby avoiding the formation of impurities in the film by elements of non-epitaxial materials and causing changes in the properties of the intrinsic material. However, after multiple rounds of epitaxial growth, impurity elements will be adsorbed and deposited on the inner walls of the cavity and components. The film formed by the long-term accumulation of impurities will become thicker and thicker, and will be released outward when heated by the source furnace or substrate stage, resulting in a higher content of background doping in the epitaxial film. Therefore, it is necessary to reduce the concentration of background impurities.

[0003] Among the current methods for reducing background impurity concentration, most of them are to reduce the vacuum degree in the cavity by using a better vacuum pump, thereby reducing the gas escape of impurity materials from the working parts and cleaning the cavity. However, replacing the vacuum pump will increase the cost, and the vacuum pump has certain usage restrictions due to the size of the cavity. In addition, the existing epitaxial chamber cavity needs to disassemble all parts when cleaning, and then assemble and degas after chemical cleaning, which consumes a lot of time, manpower and resources. At present, the cleaning by baking is generally heated to 150-250℃ outside the cavity after the equipment is assembled, so as to release the impurity gas adsorbed on the surface and inside of the cavity material as soon as possible, but the baking cleaning has the problem of long heating time and poor effect. At present, these methods of reducing the background impurity concentration are to try to remedy and reduce the impurity concentration after the background impurities are formed, and it is impossible to further reduce the vacuum degree and impurity concentration in the epitaxial chamber cavity from the source. Therefore, the existing technology still needs to be improved and developed. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a molecular beam epitaxy device for reducing background doping and a method of using the same, aiming to solve the problem that the existing methods for reducing background impurity concentration cannot further reduce the vacuum degree and impurity concentration in the epitaxial chamber cavity from the source.

[0005] The technical solution of this application is as follows: In a first aspect, the present application provides a molecular beam epitaxy device for reducing background doping, comprising an epitaxial chamber cavity in which a source furnace and a substrate table are arranged, wherein the molecular beam evaporated from the source furnace comprises an effective beam directed toward the substrate table and an ineffective beam not passing through the substrate table, wherein the device further comprises a cryogenic tube, both ends of which are exposed outside the epitaxial chamber cavity, and the portion of the cryogenic tube within the epitaxial chamber cavity is spirally wound into a curved tube for shielding the ineffective beam.

[0006] The present application can increase the adsorption area by spirally winding a curved tube in the epitaxial chamber cavity, reduce the overflow of invalid beams and impurity concentration by shielding and low-temperature adsorption, and help stabilize the vacuum degree, which is beneficial to improving the epitaxial quality.

[0007] Furthermore, the shape of the bent pipe is a spiral tube, the tube bodies of the bent pipe do not contact each other, the bending radius of two adjacent tubes in the bent pipe is the same, the top edge of the emission range of the invalid beam is tangent to the two adjacent tubes in the bent pipe, and the bottom edge of the emission range of the invalid beam is tangent to the two adjacent tubes in the bent pipe.

[0008] The present application controls the top and bottom edges of the invalid beam emission range to be tangent to the adjacent tubes in the bent tube. The tube body of the bent tube can still maintain a shielding effect on the invalid beam without the need for close abutment, thereby increasing the service life of the cryogenic tube. The molecular beams at the top and bottom edges can be acted on simultaneously by adjacent tubes, reducing overflow.

[0009] Furthermore, the top edge of the emission range of the invalid beam is tangent to the working surface boundary of the substrate stage. The present application controls the emission range of the invalid beam to avoid unnecessary dispersion caused by the extension of the invalid beam path, which is beneficial to reducing the background impurity concentration and optimizing the spatial distribution of components.

[0010] Further, the shape of the epitaxial chamber cavity is cylindrical, and the ratio of the diameter of the elbow to the inner wall diameter of the epitaxial chamber cavity is 1:10-1:20; The distance between the outermost side of the curved tube and the inner wall of the epitaxial chamber cavity is 1 / 20-1 / 40 of the diameter of the inner wall of the epitaxial chamber cavity.

[0011] The present application controls the diameter of the curved tube to match the size of the epitaxial chamber cavity to ensure a good arc effect, and is easy to adsorb while reflecting and diverging the invalid beam, which is beneficial to improving the epitaxial quality. By adjusting the bending radius and diameter of the curved tube, stress fracture is avoided, and the low-temperature adsorption range can also better act on the invalid beam and the inner wall of the epitaxial chamber cavity, which is beneficial to reducing the background impurity concentration.

[0012] Furthermore, a heating wire is inserted into the cryogenic tube. By setting the heating wire to generate heat, the cryogenic tube can be baked at high temperature in the epitaxial chamber cavity, evaporating the material adsorbed on the bent tube and the inner wall of the cavity and discharging it in time, avoiding the tedious operation of opening the cavity to clean the inner wall, and greatly shortening the equipment maintenance time.

[0013] Furthermore, the tube body structure of the cryogenic tube includes a substrate, a nitriding buffer layer and a barrier layer in sequence from the inside to the outside; The barrier layer is titanium aluminum nitride.

[0014] Furthermore, the method for preparing the cryogenic tube comprises the following steps: A tubular substrate is provided, a middle portion between two ends of the tubular substrate is bent into a spiral winding shape, and a surface pretreatment is performed on the tubular substrate to obtain a tubular body; Performing nitriding treatment on the surface of the tube body to obtain the nitriding buffer layer; growing the barrier layer on the nitrided buffer layer by atomic layer deposition; The heating wire is passed into the interior of the tube body and then connected to a power source, and both ends of the tube body are passed through the body wall of the epitaxial chamber cavity and welded together, and leak detection is performed to obtain the low-temperature tube; After the barrier layer is grown on the nitriding buffer layer by atomic layer deposition, the following steps are also included: After the barrier layer is grown, the deposition chamber is evacuated to 10 -4 Under a vacuum of the order of Pa, heat to 500°C and bake for 96 hours according to vacuum operation specifications.

[0015] Furthermore, the step of performing nitriding treatment on the surface of the tube body comprises: The tube body is placed in an ion nitriding furnace, ammonia is used as the nitriding gas, the nitriding gas pressure is maintained at 300-450 Pa, the nitriding temperature is 280-450° C., and the nitriding time is 0.5-2 h; The thickness of the nitriding buffer layer is 5-100 μm.

[0016] Further, the step of growing the barrier layer on the nitriding buffer layer by atomic layer deposition comprises: The tube body is placed in a deposition chamber, the temperature is maintained at 200° C., and the tube body is cyclically exposed to ammonia for 60 s, nitrogen purge for 20 s, a mixed precursor of tetrakisdimethylaminotitanium and trimethylaluminum for 5 s, and nitrogen purge for 20 s, and the cycle is repeated for 500-5000 times; The thickness of the barrier layer is 0.3-5 μm.

[0017] Furthermore, after growing the barrier layer on the nitriding buffer layer by atomic layer deposition, the method further comprises the following steps: After the barrier layer is grown, the deposition chamber is evacuated to 10 -4 Under a vacuum of the order of Pa, heat to 500°C and bake for 96 hours according to vacuum operation specifications.

[0018] In a second aspect, the present application further provides a method for using the molecular beam epitaxy device for reducing background doping as described above, wherein the method comprises the following steps: The heating wire is heated to 300° C. at a heating rate of 5-10° C. / min and kept at this temperature for 2-10 hours; Then, the temperature is raised to 600-800°C at a rate of 1-5°C / min and kept at this temperature. When the vacuum degree of the epitaxial chamber is reduced to 10 -5 ~10 -6 Pa, the heating is stopped, the temperature is cooled to room temperature, and then a cryogenic fluid is introduced into the cryogenic tube.

[0019] Beneficial effect: In the molecular beam epitaxy device for reducing background doping provided by the present application, a spirally wound low-temperature tube is sealed and arranged in the cavity of the epitaxial chamber. During epitaxial growth, the molecular beam that overflows from the source furnace and is not deposited on the substrate table can be blocked and adsorbed at a low temperature, thereby effectively reducing the background impurity concentration in the device, reducing pollution, helping to stabilize the vacuum degree in the cavity of the epitaxial chamber, which is beneficial to improving the epitaxial quality and facilitating the cleaning of the cavity of the epitaxial chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of the cryogenic tube and epitaxial chamber cavity of the present application.

[0021] Figure 2 This is a schematic diagram of the structure of a molecular beam epitaxy device for reducing background doping in the present application.

[0022] Figure 3 This is a schematic diagram of the tube body structure of the cryogenic tube of this application.

[0023] Explanation of reference numerals: 1. epitaxial chamber cavity; 2. source furnace; 3. substrate table; 4. cryogenic tube; 41. both ends of the cryogenic tube; 42. bent tube; 43. heating wire; 44. substrate; 45. nitriding buffer layer; 46. barrier layer; 5. ineffective beam; 6. effective beam. DETAILED DESCRIPTION

[0024] The present application provides a molecular beam epitaxy device for reducing background doping and a method for using the same. To make the purpose, technical solution and effect of the present application clearer and more specific, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] In the existing molecular beam epitaxy process, the molecular beams ejected by the source furnace 2 are ejected toward the substrate stage 3 for epitaxial growth. However, in order to ensure the uniformity of the growth of the epitaxial layer on the substrate, the source furnace 2 is generally ejected toward the substrate stage 3 at an angle, and when the evaporated molecular beams reach the substrate stage 3, the area covered by the emission range is generally larger than the substrate stage 3. Therefore, the molecular beams include invalid beams 5 that are not ejected toward the substrate stage 3. These invalid beams 5 will be ejected toward the inner wall of the epitaxial chamber cavity 1 for deposition, and may overflow to form background impurities during epitaxy. It is not only cumbersome to clean up, but also easy to increase the concentration of background impurities, affecting the purity of the subsequent epitaxial process.

[0026] For this problem, refer to Figure 1-Figure 3 The present application provides a molecular beam epitaxy device for reducing background doping, including an epitaxial chamber cavity 1 in which a source furnace 2 and a substrate stage 3 are arranged, the molecular beam evaporated from the source furnace 2 includes an effective beam 6 directed toward the substrate stage 3 and an ineffective beam 5 that does not pass through the substrate stage 3, wherein the device also includes a cryogenic tube 4, both ends 41 of the cryogenic tube are exposed outside the epitaxial chamber cavity 1, and the part of the cryogenic tube 4 in the epitaxial chamber cavity 1 is spirally wound into a curved tube 42 that blocks the ineffective beam 5.

[0027] The substrate stage 3 is disposed in a space surrounded by the curved pipe 42 , and the source furnace 2 is disposed below the curved pipe 42 .

[0028] In the molecular beam epitaxy device provided by the present application, a section of spirally wound cryogenic tube 4 is sealed in the epitaxial chamber cavity 1, so that during epitaxial growth, the molecular beam that overflows from the source furnace 2 and is not deposited on the substrate table 3 can be shielded and adsorbed at low temperature, effectively reducing the background impurity concentration in the device and reducing pollution. In addition, a high vacuum molecular pump group (not shown in the figure) is generally provided in the epitaxial chamber cavity 1, so that epitaxy can be performed at the required vacuum degree. The provided cryogenic tube 4 can also help stabilize the vacuum degree in the epitaxial chamber cavity 1, which is beneficial to improving the epitaxy quality. In addition, impurities are adsorbed on the cryogenic tube 4, which is more convenient for cleaning the epitaxial chamber cavity 1.

[0029] Specifically, refer to Figure 2, the molecular beam will diverge to form a certain emission range when it is ejected, and the position of the substrate stage 3 can only cover a part of the ejected molecular beam. At this time, the molecular beam includes the effective beam 6 directed to the substrate stage 3, and the invalid beam 5 not directed to the substrate stage 3, and the effective beam 6 directed to the substrate stage 3 may also reflect part of the invalid beam 5 (not shown in the figure). The present application uses a spirally wound bend pipe to increase the surface area of ​​the cryogenic tube 4 in the cavity, increase the adsorption capacity, and stabilize the vacuum degree. The bend pipe 42 shields the invalid beam 5 by surrounding the substrate stage 3 and adsorbs it at low temperature to avoid deposition on the inner wall of the cavity to form background doping. Moreover, the curved surface of the bend pipe 42 can also reduce the intensity and concentration of the invalid beam 5 reflected again on the bend pipe 42, improve the divergence effect after reflection, and is more easily pumped away by the high vacuum molecular pump group or adsorbed by the bend pipe 42 at low temperature, so as to further reduce the background doping.

[0030] Among them, one of the two ends 41 of the low-temperature tube can be an inlet end, and the other end is an outlet end. A low-temperature fluid can be introduced into the pipeline of the low-temperature tube 4, specifically, liquid nitrogen and other fluids that can control the temperature at the required low temperature to ensure that the low-temperature adsorption effect required by this application can be achieved.

[0031] Further, refer to Figure 2 The shape of the curved tube 42 is a spiral tube. The tube bodies of the curved tube 42 do not touch each other. The bending radii of two adjacent tubes in the spiral curved tube 42 are the same. The top edge of the emission range of the invalid beam 5 is tangent to the two adjacent tubes in the curved tube 42. The bottom edge of the emission range of the invalid beam 5 is tangent to the two adjacent tubes in the curved tube 42.

[0032] Specifically, the molecular beam evaporated from the source furnace 2 can be regarded as a cone shape, which emits from a point in the source furnace 2 to the source furnace mouth. The molecular beam is equivalent to scattering multiple rays in different directions from this point. The range covered by the rays is also the emission range of the molecular beam, and the part that does not pass through the substrate stage 3 is the emission range of the invalid beam 5. Figure 2 In the position distribution shown, the top side corresponds to the highest ray in the emission range of the invalid beam 5 , and the bottom side corresponds to the lowest ray in the emission range of the invalid beam 5 .

[0033] In the present application, by controlling the bending radius and spacing of adjacent tubes in the curved tube 42 (specifically, the spacing between two adjacent tubes of the curved tube 42 can be controlled according to the emission angle of the source furnace 2), the top and bottom sides of the emission range of the invalid beam 5 can be tangent to the adjacent tubes of the curved tube 42 respectively, ensuring that the top of the curved tube 42 is higher than the top side of the emission range of the invalid beam 5, and the bottom side is lower than the bottom side of the emission range of the invalid beam 5, and the height of the curved tube 42 can cover the injection range of the invalid beam 5 on the curved tube 42. Since the molecular beam is generally divided by the working surface boundary of the substrate stage 3 to form the effective beam 6 and the invalid beam 5, the molecular beam located at the top or bottom side is simultaneously acted on by the two adjacent tubes of the curved tube 42, the adsorption degree is higher, the overflow is reduced, and it is ensured that the invalid beam 5 within the range is surrounded by the facing surface of the curved tube 42 or is tangent to the adjacent tubes for shielding, and the degree of enclosing the invalid beam 5 can be guaranteed without deliberately setting different tube diameters.

[0034] More specifically, when performing epitaxy (low temperature adsorption) or baking cleaning, if the tube bodies of the bent tubes 42 are tightly abutted, it will be difficult to cope with the volume change caused by thermal expansion and contraction. However, through the configuration of the present application, the bent tubes 42 do not touch each other in the tube bodies, and the distance between adjacent tubes is as large as possible through tangency. In this case, the invalid beam 5 can be effectively shielded, which helps to increase the service life of the cryogenic tube 4, and when cleaning impurities, the cleaning efficiency and cleaning degree can also be improved.

[0035] Further, the top edge of the emission range of the ineffective beam 5 is tangent to the boundary of the working surface of the substrate table 3 .

[0036] In the present application, the invalid beam 5 is controlled to be ejected toward the side of the curved tube 42 close to the source furnace 2 by the top edge tangent, so as to avoid unnecessary escape caused by the extension of the path of the invalid beam 5 and reduce the risk of background impurities. Moreover, the number of turns of the spiral curved tube 42 does not need to be set too high to ensure the shielding degree, which is conducive to optimizing the spatial distribution of various components in the epitaxial chamber cavity 1.

[0037] Among them, the source furnace 2 can be symmetrically arranged according to the central axis of the spiral tube-shaped bend 42. The injection intensity of the source furnace 2 is easy to control, and the utilization rate of the bend 42 can be improved, which is beneficial to improving the uniformity and quality of the epitaxy.

[0038] Specifically, the epitaxial chamber cavity 1 can be of different shapes, and the bending radius of the bend 42 can be set according to the size of the substrate stage 3, so as to ensure that the substrate stage 3 is surrounded and the emission range of the invalid beam 5 is blocked. Preferably, the epitaxial chamber cavity 1 is cylindrical, and the central axis of the spiral-shaped bend 42 coincides with the central axis of the cylindrical epitaxial chamber cavity 1. The bend 42 has a higher degree of effect and is more likely to cooperate with the epitaxial chamber cavity 1 to achieve the effect of stabilizing the vacuum degree. For epitaxial chamber cavities 1 of different sizes, the bend 42 can adopt different tube diameters and bending radii of the tube body. The principle of use is that the bend 42 is basically wound according to the inner wall of the epitaxial chamber cavity 1, and the diameter of the bend 42 is proportional to the inner diameter of the epitaxial chamber cavity 1.

[0039] Furthermore, the shape of the epitaxial chamber cavity 1 is cylindrical (closed at both ends), and the ratio of the diameter of the bend 42 to the inner wall diameter of the epitaxial chamber cavity 1 is between 1:10-1:20. In the present application, by controlling the diameter of the bend 42 to match the size of the epitaxial chamber cavity 1, a good arc effect can be maintained within this range, and it is easy to absorb the invalid beam 5 while reflecting and diverging, avoiding strong directional reflection due to excessive or small diameter, which affects the epitaxy quality. Moreover, if the diameter of the bend 42 is too large, it will also limit the setting of the bending radius, making it difficult to match the size of the epitaxial chamber cavity 1.

[0040] Furthermore, the distance between the outermost side of the bend 42 and the inner wall of the epitaxial chamber cavity 1 is within the range of 1 / 20-1 / 40 of the diameter of the inner wall of the epitaxial chamber cavity 1. In the present application, considering that the temperature adjustment during epitaxy and cleaning is relatively frequent, the stress fracture problem caused by temperature change can be avoided by adjusting the bending radius and diameter of the bend 42. The low-temperature adsorption range can also better cover the invalid beam 5 without having too much impact on the effective beam on the substrate stage 3. At the same time, some impurities that may be deposited on the inner wall, or impurities excited by heat from the inner wall, are adsorbed in time, which is beneficial to reduce the impurity concentration while ensuring the quality of epitaxy. Moreover, the bend 42 still maintains a certain distance from the inner wall of the epitaxial chamber cavity 1, and the vacuum environment in the cavity can block the heat exchange with the outside world, preventing the outer wall of the cavity from being too cold during epitaxy, resulting in condensation of water vapor or ice.

[0041] Further, refer to Figure 1 A heating wire 43 is provided in the cryogenic tube 4. Specifically, the heating wire 43 can be made of materials such as iron-chromium-aluminum, nickel-chromium alloy, etc. that can generate heat through electrical feedthrough, and a ceramic insulating tube can be provided outside the heating wire so that the heating wire 43 and the inner wall of the cryogenic tube 4 are insulated and connected.

[0042] In the present application, a heating wire 43 is provided in the low-temperature tube 4. When the heating wire 43 is powered on, it generates heat and can generate a high temperature of 25-800°C. Through high-temperature baking, the material adsorbed on the curved tube 42 and the inner wall of the cavity can be evaporated and discharged from the inside of the epitaxial chamber cavity 1 through a high vacuum molecular pump group, thereby avoiding the tedious operation of opening the cavity to clean the inner wall, thereby greatly shortening the equipment maintenance time.

[0043] The present application proposes a method of combining the cryotube 4 with the heating wire 43, which can reduce the impurity content in the epitaxial chamber cavity 1 and thus reduce background doping. Compared with the inner wall of the cavity, the ineffective beam 5 deposited on the cryotube 4 can clean the inside of the cavity through the heating wire 43 without opening the epitaxial chamber cavity 1, which has higher cleaning efficiency and does not require cumbersome disassembly and assembly, saving manpower and cleaning time.

[0044] Further, refer to Figure 3 The tube structure of the cryotube 4 includes a substrate 44, a nitriding buffer layer 45 and a barrier layer 46 from the inside to the outside; the barrier layer 46 is titanium aluminum nitride (TiAlN). The substrate 44 can be 316L stainless steel or 304 stainless steel, which has good air tightness.

[0045] Specifically, in the present application, since the cryogenic tube 4 will gradually deposit and thicken on the surface of the cryogenic tube 4 when adsorbing impurities, a certain penetration effect will be produced on the cryogenic tube 4 at this time. By growing a flat and dense aluminum titanium nitride layer on the surface of the cryogenic tube 4, the impurities can be well blocked in the aluminum titanium nitride layer during low-temperature adsorption to avoid further penetration, especially hydrogen with strong penetration ability in the background impurities. After hydrogen is adsorbed, the aluminum titanium nitride layer contains a large number of N-, Ti- and AL-dangling bonds, which can combine with hydrogen to prevent hydrogen from continuing to penetrate. At the same time, with the larger adsorption area of ​​the bent tube 42, the hydrogen that is easy to penetrate is concentrated, reducing the penetration of hydrogen into the inner wall or continuing to penetrate on the cryogenic tube 4, making it easier to clean and discharge.

[0046] The dense film layer of aluminum titanium nitride can also prevent the penetration of other gases, thereby reducing the background impurity concentration of the epitaxial chamber cavity 1. In addition to the evaporation of impurities during high-temperature baking, the dangling bonds will also break at high temperatures, and the combined impurities will also be discharged, and the overall cleanliness level will be higher. Moreover, when the high temperature is provided by the heating wire 43, even if the cryogenic tube 4 is connected to the atmosphere, the aluminum titanium nitride coating will first react with oxygen at high temperatures to form a very thin and dense Al2O3 passivation film, so that the cryogenic tube 4 has good high-temperature oxidation resistance. In addition, the dense film layer can also prevent other gases from penetrating at the cryogenic tube 4, avoiding the penetration into the epitaxial chamber cavity 1 and causing the background impurity concentration to increase.

[0047] The present application also provides a large amount of titanium nitride and some related N dangling bonds for the substrate 44 by setting a nitriding buffer layer 45 between the substrate 44 and the aluminum titanium nitride layer, which can strengthen the bonding effect between the aluminum titanium nitride layer and the substrate 44, making the bonding ability between the aluminum titanium nitride coating and the substrate 44 stronger, which is beneficial to improving the barrier performance of aluminum titanium nitride and preventing the coating from cracking and falling off.

[0048] Furthermore, the preparation method of the cryogenic tube 4 comprises the following steps: A tubular base 44 is provided, and the middle portion between the two ends of the tubular base 44 is bent into a spiral winding shape to obtain a bent tube 42, and the surface of the tubular base 44 is pre-treated to obtain a tube body; Performing nitriding treatment on the surface of the tube body to obtain a nitriding buffer layer 45; A barrier layer 46 is grown on the nitrided buffer layer 45 by atomic layer deposition (ALD); After the heating wire 43 is passed into the interior of the tube body and connected to a power source, the two ends of the tube body are passed through the body wall of the epitaxial chamber cavity 1 and welded together, and leak detection is performed to obtain a low-temperature tube 4.

[0049] Furthermore, after the barrier layer 46 is grown, vacuuming and heating and baking may be performed.

[0050] More specifically, the method for preparing the cryogenic tube 4 comprises the following steps: S1. A tubular substrate 44 is provided, and the middle part between the two ends of the tubular substrate 44 is bent into a spiral winding shape to obtain a bent tube 42. The surface of the tubular substrate 44 is ground and polished to a mirror surface, and the tubular substrate 44 is cleaned with ethanol, acetone and deionized water in turn, and then dried in a vacuum furnace at 200° C. for standby use to obtain a tube body. In the present application, the tube body is cleaned with ethanol, acetone and deionized water in turn to achieve degreasing, desalting and de-particle cleaning, which is beneficial to the subsequent nitriding and deposition of the barrier layer 46.

[0051] S2. Place the tube body in an ion nitriding furnace, use ammonia (NH3) as the nitriding gas, maintain the nitriding gas pressure at 300-450 Pa, the nitriding temperature at 280-450°C, and the nitriding time at 0.5-2h, to obtain a nitriding buffer layer 45 with a thickness of 5-100μm. In the present application, ion nitriding can obtain an in-situ nitriding layer on the substrate 44. By preparing a nitriding buffer layer 45 of a certain thickness, it can not only enhance the barrier to gas, but also help to enhance the deposition of subsequent materials, enhance the adhesion of materials, and help to improve the bonding ability between the barrier layer 46 and the substrate 44.

[0052] S3, put the tube into the deposition chamber, keep the temperature at 200°C, expose the tube to ammonia for 60 s, nitrogen purge for 20 s, a mixed precursor of tetrakisdimethylaminotitanium and trimethylaluminum for 5 s, and nitrogen purge for 20 s, repeat 500-5000 cycles, and obtain a barrier layer 46 with a thickness of 0.3-5 μm on the nitriding buffer layer 45. Specifically, the flow ratio of tetrakisdimethylaminotitanium (TDMAT) and trimethylaluminum (TMA) in the mixed precursor can be controlled between 1:1 and 1:2. In the present application, the deposition temperature is fixed at 200°C, which can inhibit the thermal decomposition of the tetrakisdimethylaminotitanium precursor. Moreover, since the temperature control is relatively frequent, by controlling the thickness of the aluminum titanium nitride barrier layer 46 to 0.3-5 μm, under the premise of ensuring sufficient barrier effect, cracking will not occur due to stress accumulation, and the long-term bonding of the barrier layer 46 and the substrate 44 is ensured.

[0053] S4. After the barrier layer 46 is grown, the deposition chamber is pumped down to 10 -4 Under a vacuum of the order of Pa, the layer is heated to 500°C and baked for 96 hours according to vacuum operation specifications. Since the barrier layer 46 is deposited in different atmospheres during growth, in addition to physical penetration, it may also combine with impurities through chemical bonding. The chemical bonds are broken by the high temperature of baking, which is also conducive to reducing the background impurity concentration.

[0054] S5, pass the heating wire 43 wrapped with the ceramic insulating tube into the interior of the tube body, add an electric feedthrough to connect the power supply, pass the two ends of the tube body through the body wall of the epitaxial chamber cavity 1 and weld them together, check for leaks, and obtain the low-temperature tube 4. Through welding for sealing, the inner wall of the epitaxial chamber cavity 1 and the outer wall of the part of the low-temperature tube 4 in the epitaxial chamber cavity 1 can be kept in a sealed state.

[0055] The body wall through which the cryogenic tube 4 passes may specifically be the upper cover of the epitaxial chamber cavity 1, and leak detection is performed to prevent leakage problems caused by poor welding of the weld.

[0056] In the present application, by combining the nitriding buffer layer 45 in the cryogenic tube 4 with the barrier layer 46, a composite structure of a substrate 44 / nitriding buffer layer 45 / barrier layer 46 is prepared, which can block gas penetration and has good hydrogen permeability. A uniformly thick and firmly bonded aluminum titanium nitride film can be obtained on the surface of a complex-shaped substrate 44 at a tempering temperature far lower than that of stainless steel.

[0057] The present application proposes to set a cryogenic tube 4 in the vacuum epitaxial chamber cavity. The cryogenic tube 4 is combined with a nitriding buffer layer 45 and a barrier layer 46. The prepared substrate 44 / nitriding buffer layer 45 / barrier layer 46 composite structure can prevent gas from penetrating through the cryogenic tube 4, and is easy to clean after adsorbing impurities. In addition, after long-term use, a large amount of thin film exists on the inner wall of the epitaxial chamber cavity 1. When cleaning the epitaxial chamber cavity 1, first stop the supply of cryogenic fluids such as liquid nitrogen in the cryogenic tube 4, turn on the high vacuum molecular pump group in the epitaxial chamber cavity 1, slowly increase the temperature of the heating wire 43 to 600-800°C, and heat the cryogenic tube 4 by thermal radiation, which can accelerate the release of adsorbed impurities in the cavity. Under high vacuum and high temperature, the residual impurities adsorbed on the inner wall of the cavity and the outer wall of the cryogenic tube 4 will be pumped away by the high vacuum molecular pump group in the form of gas, thereby reducing the background impurity content of the epitaxial chamber cavity 1. The molecular beam epitaxy device provided in the present application can reduce the background impurity concentration in the epitaxial chamber, reduce the cavity baking time during cleaning, and eliminate the need to open the cavity to clean the inner wall, thereby greatly shortening the equipment maintenance time.

[0058] The present application also provides a method for using the molecular beam epitaxy device for reducing background doping as described above: Heat the heating wire 43 at a heating rate of 5-10°C / min to 300°C, keep the temperature at this temperature for 2-10h, then heat it to 600-800°C at a rate of 1-5°C / min, preferably 700°C, keep the temperature, observe the vacuum degree of the vacuum gauge, and when the vacuum degree of the epitaxial chamber cavity 1 drops to 10 -5 ~10 -6 Pa, the heating can be stopped and the temperature can be slowly lowered to room temperature (at a rate of 1-5°C / min) until the next use, and low-temperature fluid can be introduced to further adsorb the molecules emitted from source furnace 2.

[0059] The invention is further described below by means of specific examples.

[0060] Example 1 The molecular beam epitaxy device for reducing background doping of embodiment 1 comprises the following steps: Tubular 316L stainless steel is used, and the middle part between the two ends of the tubular 316L stainless steel is bent into a spiral shape by a bending machine, and the thread spacing, bending radius and pipe diameter of the steel pipe are controlled according to the design of the epitaxial chamber cavity 1 and the source furnace 2, and the surface is ground and polished to a mirror surface, and the tubular 316L stainless steel is cleaned with ethanol, acetone and deionized water in turn, and then dried in a vacuum furnace at 200°C for standby use to obtain a tube body; The tube body is placed in an ion nitriding furnace, and ammonia with a purity of 99.999% is used as the nitriding gas. The nitriding gas pressure is maintained at 350 Pa, the nitriding temperature is 350°C, and the nitriding time is 1.5 h, to obtain a nitriding buffer layer 45 with a thickness of 15 μm; After nitriding is completed, ALD is performed by alternately supplying a mixed precursor of 99.999% pure tetrakisdimethylaminotitanium and 99.9999% pure trimethylaluminum and 99.999% pure ammonia, and the tube is placed in a deposition chamber, the temperature is maintained at 200°C, and the tube is cyclically exposed to ammonia for 60 s, nitrogen purge for 20 s, a mixed precursor of tetrakisdimethylaminotitanium and trimethylaluminum for 5 s, and nitrogen purge for 20 s, and the cycle is repeated 1500 times to obtain a barrier layer 46 with a thickness of 2.3 μm; After the barrier layer 46 is grown, the deposition chamber is evacuated to 10 -4 Under a vacuum of the order of Pa, heat to 500°C and bake for 96 hours according to vacuum operation specifications; The heating wire 43 wrapped with ceramic insulating tube is passed into the interior of the low temperature tube 4, and the power supply is connected with the electric feedthrough. The two ends of the tube body are passed through the upper cover of the epitaxial chamber cavity 1 and welded together. Leakage detection is carried out, and the leakage rate is less than 1×10 -10 Pa·L / s, and a low temperature tube 4 is obtained.

[0061] The cryogenic tube 4, source furnace 2, substrate stage 3 and high vacuum molecular pump group prepared in Example 1 are assembled into the epitaxial chamber cavity 1 to obtain the molecular beam epitaxy device of Example 1, and the epitaxial chamber cavity 1 is evacuated to vacuum for use. In the molecular beam epitaxy device of Example 1, the substrate stage 3 is arranged in the space surrounded by the curved pipe 42, the source furnace 2 is arranged below the curved pipe 42, and the emission angle of the source furnace 2 and the position of the substrate stage 3 are adjusted to ensure that the top edge of the emission range of the invalid beam 5 is tangent to the working surface boundary of the substrate stage and the two adjacent tubes in the curved pipe 42 at the same time, and the bottom edge of the emission range of the invalid beam 5 is tangent to the two adjacent tubes in the curved pipe 42, and the curved pipe 42 blocks the invalid beam 5 from being emitted to the inner wall of the epitaxial chamber cavity 1. Among them, the bending radius of two adjacent tubes in the curved tube 42 is the same; the shape of the epitaxial chamber cavity 1 is a cylinder with closed ends, the central axis of the spiral curved tube 42 coincides with the central axis of the cylindrical epitaxial chamber cavity 1, the ratio of the tube diameter of the curved tube 42 to the inner wall diameter of the epitaxial chamber cavity 1 is 1:15, and the distance between the outermost side of the curved tube 42 and the inner wall of the epitaxial chamber cavity 1 is 1 / 30 of the inner wall diameter of the epitaxial chamber cavity 1.

[0062] The method of using the molecular beam epitaxy device of Example 1 is as follows: heating the heating wire 43, heating it to 300°C at a heating rate of 5-10°C / min, keeping it at this temperature for 2-10h, then heating it to 600-800°C at a heating rate of 1-5°C / min, preferably to 700°C, keeping it at this temperature, observing the vacuum degree of the vacuum gauge, and when the vacuum degree of the epitaxial chamber cavity 1 drops to 10 -5 ~10 -6 Pa, the heating can be stopped and the temperature can be slowly cooled to room temperature (at a rate of 1-5°C / min) until the next use, and liquid nitrogen can be introduced to further adsorb the molecules emitted from source furnace 2.

[0063] The performance of the molecular beam epitaxy device prepared in Example 1 was tested. Specifically, after heating, baking and cleaning by the heating wire 43, the epitaxial chamber cavity 1 was evacuated to the required vacuum degree, and then liquid nitrogen was introduced into the low-temperature tube 4. The vacuum degrees before and after the liquid nitrogen treatment are shown in Table 1.

[0064] Table 1 Before treatment (Torr) After treatment (Torr) Ultimate vacuum 9E-12 8E-12 Daily vacuum degree 6E-10 5E-11 Mass spectrometry hydrogen content equivalent pressure 3E-11 4E-13 By comparison, it can be found that through the molecular beam epitaxy device provided in Example 1 of the present application, the vacuum degree in the epitaxial chamber cavity 1 can be reduced by 1-2 orders of magnitude before and after processing, which effectively reduces the content of background impurities, can meet the use requirements of molecular beam epitaxy, and is conducive to improving the epitaxy quality.

[0065] It should be understood that the application of the present application is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made according to the above description, and all these improvements and changes should fall within the scope of protection of the present application.

Claims

1. A molecular beam epitaxy device for reducing background doping, comprising an epitaxial chamber cavity (1) in which a source furnace (2) and a substrate table (3) are arranged, wherein the molecular beam evaporated by the source furnace (2) comprises an effective beam (6) directed toward the substrate table (3) and an ineffective beam (5) not passing through the substrate table (3), characterized in that: It also comprises a cryogenic tube (4), both ends (41) of the cryogenic tube being exposed outside the epitaxial chamber cavity (1), and the portion of the cryogenic tube (4) inside the epitaxial chamber cavity (1) being spirally wound to form a curved tube (42) that shields the ineffective beam (5).

2. The molecular beam epitaxy device for reducing background doping according to claim 1, characterized in that: The shape of the curved tube (42) is a spiral tube; the tube bodies of the curved tube (42) do not contact each other; the bending radii of two adjacent tubes in the curved tube (42) are the same; the top edge of the emission range of the invalid beam (5) is tangent to the two adjacent tubes in the curved tube (42); and the bottom edge of the emission range of the invalid beam (5) is tangent to the two adjacent tubes in the curved tube (42).

3. The molecular beam epitaxy device for reducing background doping according to claim 2, characterized in that: The top edge of the emission range of the ineffective beam (5) is tangent to the boundary of the working surface of the substrate table (3).

4. The molecular beam epitaxy device for reducing background doping according to claim 2, characterized in that: The epitaxial chamber cavity (1) is cylindrical in shape, and the ratio of the diameter of the curved tube (42) to the inner wall diameter of the epitaxial chamber cavity (1) is 1:10-1:20; The distance between the outermost side of the curved tube (42) and the inner wall of the epitaxial chamber cavity (1) is 1 / 20-1 / 40 of the diameter of the inner wall of the epitaxial chamber cavity (1).

5. The molecular beam epitaxy device for reducing background doping according to claim 1, characterized in that: A heating wire (43) is inserted into the low-temperature tube (4).

6. The molecular beam epitaxy device for reducing background doping according to claim 5, characterized in that: The tube body structure of the cryogenic tube (4) comprises, from the inside to the outside, a base body (44), a nitriding buffer layer (45) and a barrier layer (46); The barrier layer (46) is aluminum titanium nitride.

7. The molecular beam epitaxy device for reducing background doping according to claim 6, characterized in that: The method for preparing the cryogenic tube (4) comprises the following steps: A tubular base (44) is provided, a middle portion between two ends of the tubular base (44) is bent into a spiral winding shape, and a surface pretreatment is performed on the tubular base (44) to obtain a tubular body; Performing nitriding treatment on the surface of the tube body to obtain the nitrided buffer layer (45); Growing the barrier layer (46) on the nitrided buffer layer (45) by atomic layer deposition; The heating wire (43) is passed into the interior of the tube body and connected to a power source, and both ends of the tube body are passed through the wall of the epitaxial chamber cavity (1) and welded together, and leak detection is performed to obtain the low-temperature tube (4); After growing the barrier layer (46) on the nitriding buffer layer (45) by atomic layer deposition, the method further comprises the following steps: After the barrier layer (46) is grown, the deposition chamber is evacuated to 10 -4 Under a vacuum of the order of Pa, heat to 500°C and bake for 96 hours according to vacuum operation specifications.

8. The molecular beam epitaxy device for reducing background doping according to claim 7, characterized in that: The step of performing nitriding treatment on the surface of the tube body comprises: The tube body is placed in an ion nitriding furnace, ammonia is used as the nitriding gas, the nitriding gas pressure is maintained at 300-450 Pa, the nitriding temperature is 280-450° C., and the nitriding time is 0.5-2 h; The thickness of the nitriding buffer layer (45) is 5-100 μm.

9. The molecular beam epitaxy device for reducing background doping according to claim 7, characterized in that: The step of growing the barrier layer (46) on the nitriding buffer layer (45) by atomic layer deposition comprises: The tube body is placed in a deposition chamber, the temperature is maintained at 200° C., and the tube body is cyclically exposed to ammonia for 60 s, nitrogen purge for 20 s, a mixed precursor of tetrakisdimethylaminotitanium and trimethylaluminum for 5 s, and nitrogen purge for 20 s, and the cycle is repeated for 500-5000 times; The barrier layer (46) has a thickness of 0.3-5 μm.

10. A method for using the molecular beam epitaxy device for reducing background doping according to any one of claims 5 to 9, characterized in that: The following steps are involved: The heating wire (43) is heated to 300°C at a heating rate of 5-10°C / min, and kept at this temperature for 2-10 hours; Then, the temperature is raised to 600-800°C at a rate of 1-5°C / min and kept at this temperature. When the vacuum degree of the epitaxial chamber (1) is reduced to 10 -5 ~10 -6 Pa, the heating is stopped, the temperature is cooled to room temperature, and a low-temperature fluid is then introduced into the low-temperature tube (4).

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