Method for manufacturing epitaxial structure, epitaxial structure and semiconductor device
By using variable-temperature annealing and perpendicular magnetic field treatment on the counter-rotating magnet ferrite magnetic layer, the crystal defect problem in the epitaxial structure was solved, high-quality epitaxial layer fabrication was achieved, and the performance and reliability of semiconductor devices were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHENGDU ZHIXIN ELECTRONIC TECH CO LTD
- Filing Date
- 2026-02-26
- Publication Date
- 2026-06-09
Smart Images
Figure CN122180304A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of semiconductor technology, and in particular to a method for preparing an epitaxial structure, the epitaxial structure, and a semiconductor device. Background Technology
[0002] Epitaxial growth is a crucial process for growing a single-crystal thin film along a specific crystal orientation on a single-crystal substrate, and it forms the foundation of semiconductor, optoelectronic, and high-performance integrated circuit manufacturing. As devices evolve towards higher performance, higher integration, and greater multifunctionality, near-limit requirements are placed on the crystal quality, interface steepness, and electrical performance of complex epitaxial structures such as heterojunctions, superlattices, and strained silicon. However, the fabrication of high-quality epitaxial structures consistently faces fundamental challenges stemming from lattice mismatch and differences in thermal expansion coefficients. This directly leads to high-density dislocations, stacking faults, and even cracks in the epitaxial layer.
[0003] Annealing, as a key post-processing step in epitaxial growth, aims to repair lattice damage during growth, activate dopants, and improve film density and electrical properties. Traditional annealing is often a simple, single-stage isothermal annealing process, which is insufficient in releasing internal stress and repairing defects, thus hindering the improvement of magnetic properties. Summary of the Invention
[0004] The technical problem to be solved by this disclosure is to overcome the above-mentioned defects in the prior art and provide a method for preparing an epitaxial structure, an epitaxial structure, and a semiconductor device.
[0005] This disclosure solves the above-mentioned technical problems through the following technical solution:
[0006] The first aspect of this disclosure provides a method for preparing an epitaxial structure, comprising the following steps:
[0007] In the reaction chamber, a magnetic layer of gyromagnetic ferrite is epitaxially grown on a semiconductor substrate; wherein the magnetic layer of gyromagnetic ferrite has in-plane uniaxial magnetic anisotropy, and the easy magnetization axis is parallel to the surface of the semiconductor substrate.
[0008] The semiconductor substrate is placed in an annealing chamber for variable temperature annealing, and a magnetic field perpendicular to the surface of the semiconductor substrate is applied in the annealing chamber to forcibly change the easy magnetization axis from parallel to the substrate surface to perpendicular to the substrate surface; wherein, the variable temperature annealing process is to subject the semiconductor substrate to at least one temperature change process between a first temperature and a second temperature, wherein the first temperature is higher than the second temperature.
[0009] Optionally, the second temperature is lower than the Curie temperature of the magnetic layer, and the preparation method further includes: stopping the application of a magnetic field in the annealing chamber in response to the temperature of the semiconductor substrate cooling to below a third temperature; wherein the third temperature is lower than the Curie temperature and higher than the second temperature.
[0010] Optionally, the semiconductor substrate undergoes the temperature change process a range of 2 to 20 times.
[0011] Optionally, the first temperature is 50°C to 100°C higher than the growth temperature of the magnetic layer.
[0012] Optionally, the second temperature is 100°C to 200°C lower than the growth temperature of the magnetic layer.
[0013] Optionally, placing the semiconductor substrate in the annealing chamber for variable temperature annealing specifically includes: automatically transferring the semiconductor substrate from the reaction chamber to the annealing chamber for variable temperature annealing.
[0014] Optionally, the strength of the magnetic field applied in the annealing chamber is in the range of 1T to 1.5T.
[0015] Optionally, the gyromagnetic ferrite is yttrium iron garnet ferrite.
[0016] A second aspect of this disclosure provides an epitaxial structure prepared according to the preparation method described in the first aspect.
[0017] A third aspect of this disclosure provides an extensional structure comprising:
[0018] Semiconductor substrates; and
[0019] A magnetic layer of gyromagnetic ferrite epitaxially grown on the semiconductor substrate;
[0020] The magnetic layer of the gyromagnetic ferrite has perpendicular magnetic anisotropy, and its easy magnetization axis is perpendicular to the surface of the semiconductor substrate.
[0021] A fourth aspect of this disclosure provides a semiconductor device including an epitaxial structure as described in the second or third aspect.
[0022] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of this disclosure.
[0023] The positive and progressive effects of this disclosure are as follows: For a magnetic layer of gyromagnetic ferrite with in-plane uniaxial magnetic anisotropy and an easy magnetization axis parallel to the surface of the semiconductor substrate, a variable temperature annealing process is performed on it, which strongly promotes the recombination of atoms and defects, effectively disintegrating and weakening the old in-plane magnetic anisotropy structure. On this basis, by applying a magnetic field perpendicular to the surface of the semiconductor substrate in the annealing chamber, the easy magnetization axis of the magnetic layer can be corrected, so that it is forcibly changed from being parallel to the surface of the semiconductor substrate to being perpendicular to the surface of the semiconductor substrate, thereby realizing the subversion and reconstruction of magnetic properties. Attached Figure Description
[0024] Figure 1 A flowchart illustrating a method for preparing an epitaxial structure, provided as an exemplary embodiment of this disclosure;
[0025] Figure 2 A schematic diagram of a layered structure of an epitaxial structure provided for an exemplary embodiment of this disclosure;
[0026] Figure 3 A schematic diagram illustrating the effect of variable temperature annealing on correcting easily magnetized shafts, provided as an exemplary embodiment of this disclosure;
[0027] Figure 4 A schematic diagram of the temperature-time curve of a YIG thin film subjected to variable temperature annealing under a magnetic field, provided as an exemplary embodiment of this disclosure;
[0028] Figure 5 A schematic diagram of the magnetic field strength-time curve of a YIG thin film subjected to variable temperature annealing under a magnetic field, provided as an exemplary embodiment of this disclosure;
[0029] Figure 6 This is a schematic diagram of the structure of a microwave circulator provided as an exemplary embodiment of the present disclosure. Detailed Implementation
[0030] The present disclosure is further illustrated below by way of embodiments, but the present disclosure is not limited to the scope of the embodiments described herein.
[0031] The prefixes such as "first" and "second" used in this disclosure are merely for distinguishing different descriptive objects and do not limit the position, order, priority, quantity, or content of the described objects. The use of ordinal numbers and other prefixes used to distinguish descriptive objects in this disclosure does not constitute a limitation on the described objects. The description of the described objects is given in the claims or the context of the embodiments, and should not be construed as an unnecessary limitation. Furthermore, in the description of this embodiment, unless otherwise stated, "multiple" means two or more.
[0032] For magnetic layers with in-plane uniaxial magnetic anisotropy, isothermal annealing at a single constant temperature can partially improve crystal quality and induce some magnetic anisotropy, but its ability to repair the microstructure is insufficient. The directional alignment of magnetic ions is completed during a single cooling process, which may be pinned by residual defects, resulting in insufficient induced magnetic anisotropy and poor uniformity. In other words, isothermal annealing has limited ability to repair deep-seated bulk and point defects (such as oxygen vacancies). Thin films have many defects, making it difficult to reduce the ferromagnetic resonance linewidth to the ideal level. Even with very high temperatures, only a limited driving force for atomic migration can be provided, which has some effect on repairing point defects, but it is completely unable to provide a driving force sufficient to break the original in-plane magnetic anisotropy and rebuild perpendicular anisotropy. Its thermodynamic driving force is insufficient to overcome the huge energy barrier constructed by shape anisotropy and the established crystal texture, and therefore it is completely powerless to change the direction of the easy magnetization axis.
[0033] In some examples, magnetic layers with in-plane uniaxial magnetic anisotropy are subjected to magnetic field annealing. However, for cases where the easy magnetization axis is parallel to the semiconductor substrate surface, the driving force generated by magnetic field annealing is insufficient to overturn and reconstruct the magnetic properties. This means it is difficult to drive large-scale, long-distance migration and rearrangement of magnetic ions and lattice defects, and difficult to pull the easy magnetization axis out of the semiconductor substrate surface and make it perpendicular to the semiconductor substrate surface.
[0034] The defect pinning effect refers to the strong pinning of magnetic domain walls by residual defects within the thin film, hindering the overall reversal of the magnetic moment under a perpendicular magnetic field. Neither the aforementioned isothermal annealing nor magnetic field annealing can completely eliminate these pinning points, resulting in weak and uneven induced perpendicular anisotropy. Ultimately, this often only tilts the easy magnetization axis, failing to achieve complete, stable, and strong perpendicular magnetic anisotropy. In other words, for magnetic layers already possessing strong in-plane magnetic anisotropy, the aforementioned isothermal annealing and magnetic field annealing can only improve their magnetic properties to a limited extent, failing to achieve a radical change in performance, i.e., they cannot forcibly shift the easy magnetization axis from in-plane to out-of-plane. Based on this, embodiments of this disclosure provide a preparation method, particularly an annealing method, capable of forcibly shifting the easy magnetization axis of a magnetic layer from in-plane to out-of-plane.
[0035] Figure 1 This is a schematic flowchart illustrating a method for preparing an epitaxial structure, provided as an exemplary embodiment of this disclosure. Figure 1 As shown, an exemplary embodiment of this disclosure provides a method for preparing an epitaxial structure that may include the following steps S101-S102:
[0036] Step S101: In the reaction chamber, a magnetic layer of gyromagnetic ferrite is epitaxially grown on a semiconductor substrate; wherein the magnetic layer of gyromagnetic ferrite has in-plane uniaxial magnetic anisotropy, and the easy magnetization axis is parallel to the surface of the semiconductor substrate. In practical applications, semiconductor substrates such as GaAs, GaN, SiC, InP, Si, or SiO2 can be used.
[0037] In one optional implementation, the gyromagnetic ferrite is yttrium iron garnet ferrite (YIG), and its magnetic layer can be referred to as a YIG thin film. In this implementation, epitaxial growth is performed using metal-organic chemical vapor deposition (MOCVD). Step S101 specifically includes: placing the semiconductor substrate in a reaction chamber, heating it to the growth temperature, and introducing both the precursor gas and the reaction gas into the reaction chamber to react and epitaxially grow the YIG thin film on the surface of the semiconductor substrate.
[0038] The precursor gas includes organic compounds of yttrium (Y) and iron (Fe). In some examples, the organic compound gas of Y is (tris)methylcyclopentadiene yttrium C. 18 H x Y, where x typically has values of 9, 21, etc. In some examples, the organic compound gas of Y is tris(cyclopentadienyl)yttrium C. 15 H 15 Y. In some examples, the organic compound gas of Fe is isopropoxy iron C. a H b FeO c Here, typical values for 'a' are 3, 9, etc., typical values for 'b' are 8, 21, etc., and typical values for 'c' are 1, 3, etc. In some examples, hydrogen, nitrogen, or other inert gases are used as the reactant gas.
[0039] In a specific example, using hydrogen (H2) as the reactant gas, the typical reaction formula is:
[0040] C 18 H x Y + C a H b FeO c + H2 = Y3Fe5O 12 + CO2 +H2O;
[0041] Among the reaction products, Y3Fe5O 12This refers to YIG, typically a single crystal, grown on a semiconductor substrate in a layered structure. In the above reaction formula, the proportions of CO2 and H2O vary depending on the precursor and reactant gases, and both are discharged as waste gases from the MOCVD reaction chamber. If other reactant gases, such as nitrogen (N2), will generate other waste gases such as NO2. This is achieved by controlling the temperature of the reaction chamber, the temperature of the semiconductor substrate, and the precursor gas CO2. 18 H x Y and C a H b FeO c The growth rate of YIG can be controlled by the flow rate and pressure of the reactant gas H2, etc.
[0042] Figure 2 This illustrates a layered structure used in GaAs HBT epitaxial structures. Figure 2 In the example shown, the substrate structure using GaAs HBT, from bottom to top, consists of: a semi-insulating GaAs substrate, an AlGaAs superlattice buffer layer, collector and sub-collector layers, a GaAs base layer, an InGaP emitter layer, a GaAs sub-emitter layer, a GaAs ohmic contact layer, a metal layer M1, an insulating layer, a magnetic metal buffer layer, a YIG magnetic layer Y1, a magnetic metal buffer layer, a metal layer M2, and a passivation layer. Figure 2 In this GaAs chip, the YIG magnetic layer Y1 is located between the metal layer and the substrate, requiring the fabrication of buffer layers between the magnetic layer and the metal layer, and between the magnetic layer and the substrate. If the lattice matching is good, buffer layers may not be necessary. The buffer layer between the magnetic layer and the metal layer serves as insulation; typically, it can be a Si3N4 insulating layer between the metal layers M1 and M2, fabricated using existing technology. The buffer layer between the magnetic layer and the substrate can be an AlGaAs superlattice buffer layer fabricated on a GaAs substrate using existing technology.
[0043] In an optional implementation, step S101 further includes: providing a dopant into the reaction chamber to epitaxially grow a magnetic layer of gyromagnetic ferrite containing the doped element. In specific implementations, the doping concentration can be precisely controlled by controlling the pressures of the precursor gas, the reactant gas, and the dopant.
[0044] In this implementation, rare earth elements or other elements can be introduced for doping, typically such as cerium (Ce), terbium (Tb), gadolinium (Gd), lutetium (Lu), and dysprosium (Dy). 3+ , gallium Ga 3+ Aluminum (Al) 3+ Silicon (Si) 4+ Doping elements such as cobalt (Co), zinc (Zn), and scandium (Sc) require the addition of corresponding rare earth elements or other elemental dopants during the MOCVD reaction process.
[0045] To improve the performance of YIG thin films in superconductivity, magnetism, and other aspects, some examples use rare earth elements such as cerium (Ce), terbium (Tb), gadolinium (Gd), and lutetium (Lu) to replace Y; and in some examples, the rare earth element dysprosium (Dy) is used. 3+ , gallium Ga 3+ Aluminum (Al) 3+ Silicon (Si) 4+ Replace Fe.
[0046] In a specific example, introducing elemental silicon (Si) for doping requires adding a silicon-Si dopant during the reaction process, typically such as silane (Si). x H y In this mixture, x and y can have various ratios, such as x=1, y=4; x=2, y=6; x=3, y=8, etc., typically represented by silane SiH4. A typical reaction formula is:
[0047] C 18 H x Y + C a H b FeO c + SiH4 + H2 = Y3Fe5Si z O 12 + CO2 +H2O;
[0048] Where z is the doping concentration, typically 1 × 10⁻⁶. 18 / cm 3 .
[0049] In some examples, rare earth elements are introduced for doping, which requires the addition of dopants such as alkane, methyl, or ethyl compounds during the reaction process. For example, trimethyl rare earth reaction gas Ln(CH3)3 or triethyl rare earth reaction gas Ln(C2H5)3 can be added. Ln can be rare earth elements such as Sc, Y, La, or Lu.
[0050] In this implementation, the performance of the magnetic layer of the gyromagnetic ferrite can be optimized by doping with other elements. Typically, for microwave applications, cobalt (Co), zinc (Zn), and scandium (Sc) doping can improve the Curie temperature and permeability of YIG, thereby optimizing the high-frequency magnetic properties of the YIG thin film. Typically, for optoelectronic applications, Si... 4+ Doping can reduce absorption and improve the optical insertion loss of YIG thin films.
[0051] Step S102: The semiconductor substrate is placed in an annealing chamber for variable-temperature annealing, and a magnetic field perpendicular to the surface of the semiconductor substrate is applied in the annealing chamber to forcibly change the easy magnetization axis from parallel to the substrate surface to perpendicular to the substrate surface. The variable-temperature annealing process involves subjecting the semiconductor substrate to at least one temperature change between a first temperature and a second temperature, where the first temperature is higher than the second temperature.
[0052] The variable temperature annealing process in this embodiment generates periodic and enormous thermal stress through the alternation of high and low temperatures. This thermal shock effect provides a dynamic drive that far exceeds that of the above-mentioned isothermal annealing and magnetic field annealing processes. It can strongly promote the recombination of atoms and defects, effectively disintegrating and weakening the old in-plane magnetic anisotropy structure. On this basis, by applying a magnetic field perpendicular to the surface of the semiconductor substrate in the annealing chamber, the easy magnetization axis of the magnetic layer can be corrected, so that it is forcibly changed from being parallel to the surface of the semiconductor substrate to being perpendicular to the surface of the semiconductor substrate.
[0053] In such Figure 3 In the example shown, the semiconductor substrate 51 is placed in an annealing chamber for variable temperature annealing, and a magnetic field with the direction of A1 is applied in the annealing chamber, causing the easy magnetization axis to change from being parallel to the surface of the semiconductor substrate 51 to being perpendicular to the surface of the semiconductor substrate 51. The direction of A1 is perpendicular to the surface of the semiconductor substrate 51.
[0054] In some examples, the magnetic field applied in the annealing chamber is a pulsed magnetic field. Utilizing the transient peak ultra-high magnetic field of the pulsed magnetic field to correct the easy magnetization axis can reduce the time required to apply the magnetic field.
[0055] In one optional implementation, the second temperature is lower than the Curie temperature of the magnetic layer, and the fabrication method further includes: stopping the application of a magnetic field in the annealing chamber in response to the semiconductor substrate cooling to below a third temperature. The third temperature is lower than the Curie temperature but higher than the second temperature. In specific implementations, the third temperature can be set according to the critical region of the Curie temperature; for example, the third temperature can be set to be 1 K lower than the Curie temperature. In some examples, the Curie temperature Tc of the YIG thin film is approximately 560 K or 287 °C.
[0056] In this implementation, when the temperature of the semiconductor substrate drops below the Curie temperature of the magnetic layer, the ferromagnetic order of the magnetic layer begins to solidify, and the directional alignment of the magnetic moments is solidified and frozen in the vertical direction. At this point, the application of a magnetic field in the annealing chamber can be stopped.
[0057] It should be noted that the magnetic field strength applied in the annealing chamber must be strong enough to overcome thermal disturbances and material anisotropy. Higher magnetic field strength results in a stronger driving force for domain magnetic moment alignment, leading to a more significant effect. In some examples, the magnetic field strength applied in the annealing chamber typically needs to be above 1T. Considering the increased coil volume due to the increased magnetic field, using 1T to 1.5T is appropriate. Furthermore, the magnetic field applied in the annealing chamber needs to be highly uniform; otherwise, it will lead to anisotropic non-uniformity and performance degradation. In some examples, the uniformity of the magnetic field within the semiconductor substrate is better than 80%.
[0058] In some examples, the first temperature is 50°C to 100°C higher than the growth temperature of the magnetic layer. In some examples, the second temperature is 100°C to 200°C lower than the growth temperature of the magnetic layer. In some examples, the growth temperature of the magnetic layer is 600°C to 800°C.
[0059] In practical applications, the semiconductor substrate undergoing a temperature change process between a first temperature and a second temperature is insufficient to completely overcome the strong shape anisotropy and in-plane horizontal magnetic anisotropy. It needs to undergo this temperature change process multiple times for iterative repair. Each temperature change process is a training for the vertical magnetic anisotropy. After multiple trainings, the vertical magnetic anisotropy is continuously strengthened and accumulated, eventually stably overpowering other magnetic anisotropies and becoming dominant.
[0060] In some examples, the semiconductor substrate undergoes 2 to 20 of the above-mentioned temperature change processes. Figure 4 This is used to illustrate the temperature-time curve of a YIG thin film undergoing variable temperature annealing under a magnetic field. Figure 5 This is used to illustrate the magnetic field strength-time curve of a YIG thin film undergoing variable temperature annealing under a magnetic field.
[0061] The process of the above-mentioned variable temperature annealing treatment is described in detail below:
[0062] First, the magnetic domains are activated in a high-temperature environment. After the semiconductor substrate has grown, it is immediately placed in an annealing chamber. The temperature in the annealing chamber is briefly higher than the growth temperature; it cannot be too high, otherwise it will damage the thin film structure. The annealing chamber must not contain reactive or precursor gases, but it can contain annealing auxiliary gases such as oxygen. In this high-temperature environment, the thin film atoms acquire high migration capabilities, allowing for deep repair of crystal defects before magnetic domain rearrangement and changes in the easy magnetization axis. This typically involves reducing the pinning effect of dislocations and grain boundaries on the domain walls, weakening the various binding forces that maintain the existing in-plane magnetic anisotropy, and enabling the magnetic domains to move.
[0063] Next, a magnetic field is applied during the high-temperature stage to rearrange the magnetic domains and the easy magnetization axis. After activating the magnetic domains, the easy magnetization axis of the magnetic layer is corrected by applying a magnetic field perpendicular to the surface of the semiconductor substrate. This perpendicular magnetic field can be a magnetic ion of the magnetic layer, such as Fe. 3+ Once the reconfiguration energy is provided to activate the magnetic moments, the magnetic domains can break free from the constraints of their original magnetic moment orientation and be forcibly changed from parallel to perpendicular. After this stage is completed, the easy magnetization axis of the magnetic layer is in a direction perpendicular to the surface of the semiconductor substrate, but it is not stable and is in a metastable state.
[0064] The easy magnetization axis of the magnetic layer is then cured during the cooling phase. During the cooling phase, the direction and intensity of the applied vertical magnetic field must remain constant, especially when cooling down to the critical region of the Curie temperature Tc, so that the easy magnetization axis will be cured during the cooling process.
[0065] As the temperature of the semiconductor substrate decreases further, moving away from the Curie temperature Tc, the easy magnetization axis of the magnetic layer gradually solidifies, but it is still not stable enough. Some magnetic domains may return to the horizontal direction or deviate from the vertical direction. Therefore, it is necessary to repeat the above process to gradually solidify the magnetic domains and the easy magnetization axis, and finally change the easy magnetization axis from being parallel to the surface of the semiconductor substrate to being perpendicular to the surface of the semiconductor substrate, thereby completely changing the magnetic properties of the magnetic layer.
[0066] Therefore, the above-mentioned variable-temperature annealing process can also be called a magnetically controlled variable-temperature cycle. The following example compares and illustrates the magnetically controlled variable-temperature cycle with the above-mentioned isothermal annealing process:
[0067] First, samples were prepared by epitaxially growing three different types of YIG thin films on a GaAs substrate, resulting in samples A, B, and C. The easy magnetization axes of all samples were parallel to the substrate surface. Specifically:
[0068] Sample A: Undoped pure YIG thin film;
[0069] Sample B: Doped with Tm 3+ YIG thin film (Tm:YIG); wherein, Tm 3+ Doping with YIG can increase the magnetic anisotropy of YIG thin films;
[0070] Sample C: Al-doped 3+ YIG thin film (Al:YIG); wherein, Al 3+ Partial Fe Substitution 3+ This can reduce the saturation magnetization Ms, thereby weakening the in-plane magnetic anisotropy and indirectly promoting the reversal of the easy magnetization axis.
[0071] Magnetically controlled variable temperature cycle: Ten complete cycles from 700°C to 500°C are performed in an oxygen atmosphere. Each cycle includes: heating to 700°C at a rate of 50°C / min and holding for 10 minutes; cooling to 500°C at a rate of 50°C / min and holding for 5 minutes; and applying a magnetic field perpendicular to the substrate surface in the annealing chamber.
[0072] The samples were treated with magnetically controlled variable temperature cycling and isothermal annealing at 700℃, respectively. The performance comparison results are shown in Table 1. In the table, Ms is the saturation magnetization in kA / m, Hk is the perpendicular anisotropic field in Oe, and ΔH is the ferromagnetic resonance linewidth in Oe.
[0073] Table 1
[0074]
[0075] Referring to Table 1, for sample A, isothermal annealing can only improve crystallization to a limited extent and cannot provide any magnetic anisotropy guidance. The easily magnetized axis maintains the in-plane orientation during growth. Magnetically controlled variable temperature cycling can effectively repair defects and achieve strong perpendicular magnetic anisotropy and extremely low loss in conjunction with the magnetic field.
[0076] For sample B, during isothermal annealing, Tm 3+ The magnetic anisotropy is randomly distributed, making it impossible to form macroscopic perpendicular magnetic anisotropy, and the defect leads to high losses; Tm 3+ The magnetic anisotropy and the magnetically controlled variable temperature cycle work together perfectly to achieve extremely high Hk while maintaining low loss.
[0077] For sample C, during isothermal annealing, low Ms cannot spontaneously lead to perpendicular magnetic anisotropy, and the easy magnetization axis is still dominated by shape anisotropy, which is in-plane direction; during magneto-controlled variable temperature cycling, low Ms combined with high-quality crystal structure, under the guidance of magnetic field, stable perpendicular magnetic anisotropy and excellent microwave performance are achieved.
[0078] In some examples, step S202 specifically includes: automatically transferring the semiconductor substrate from the reaction chamber to the annealing chamber in a vacuum environment for variable temperature annealing. In some examples, step S202 specifically includes: actively transferring the semiconductor substrate from the reaction chamber to the annealing chamber in a protective atmosphere for variable temperature annealing.
[0079] By establishing an automated transport path between the reaction chamber and the annealing chamber, the semiconductor substrate is kept in a vacuum or protective atmosphere environment after growth until annealing is completed. This not only effectively avoids oxidation and contamination caused by atmospheric exposure and maintains the cleanliness and integrity of the interface, but also significantly reduces the ferromagnetic resonance linewidth of the magnetic layer, increases the saturation magnetization, and obtains more uniform magnetic properties.
[0080] In some examples, to obtain a magnetic layer with its easy magnetization axis parallel to the surface of the semiconductor substrate, a magnetic field is applied in the reaction chamber during the epitaxial growth of the magnetic layer of the gyromagnetic ferrite, and this magnetic field has a component parallel to the surface of the semiconductor substrate. In practical applications, the magnetic field applied in the reaction chamber is a uniform magnetic field, and the semiconductor substrate rotates at a constant speed during the growth process.
[0081] In some examples, the magnetic field is generated by an electromagnet outside the reaction chamber, such as a C-shaped electromagnet or a Helmholtz coil, and the strength of the generated magnetic field ranges from 0.1T to 0.5T, with a uniformity better than 90%. In some examples, the magnetic field applied inside the reaction chamber is a constant magnetic field, a pulsed magnetic field, or a scanning magnetic field.
[0082] By applying a magnetic field with a magnetic field component parallel to the surface of the semiconductor substrate during epitaxial growth, the surface migration and lattice arrangement of reactant gas atoms in the reaction chamber can be affected, thereby changing the crystal orientation. Even on untextured semiconductor substrates such as GaAs, GaN, SiC, InP, Si, and SiO2, in-plane uniaxial magnetic anisotropy can be induced, thereby growing a magnetic layer of gyromagnetic ferrite with strong crystallographic texture. In other words, a high-quality magnetic layer of gyromagnetic ferrite with an easy magnetization axis parallel to the surface of the semiconductor substrate can be grown efficiently.
[0083] The magnetic field applied during epitaxial growth can suppress the convection of reactive and precursor gases, improve epitaxial uniformity, and enhance film quality. Specifically, in MOCVD vapor phase epitaxy, the Lorentz force suppresses thermal convection of charged reactive atoms on the semiconductor substrate surface. The magnetic field, by influencing surface mobility and nucleation barriers, can increase nucleation density, refine grain size, and improve the density of the magnetic layer. Compared to growing without a magnetic field, a magnetic layer closer to a single crystal can be obtained.
[0084] The magnetic field applied during epitaxial growth can also induce oriented growth. Specifically, for precursor and reactant gases with anisotropic magnetic susceptibility, when reacting in a magnetic field, the reaction products will undergo rotation or directional growth in order to align their easy magnetization axis with the direction of the external magnetic field and reduce the static magnetic energy of the system. That is, the magnetic field will cause the grains to tend to align with a specific crystal axis along the direction of the magnetic field in order to minimize the magnetization energy. This allows magnetic layers with strong crystallographic texture to be induced to grow even on textureless semiconductor substrates such as GaAs and Si.
[0085] In some examples, the direction of the magnetic field applied in the reaction chamber is parallel to the surface of the semiconductor substrate. In other examples, there is an angle between the direction of the magnetic field applied in the reaction chamber and the surface of the semiconductor substrate; that is, the magnetic field has not only a component parallel to the surface of the semiconductor substrate but also a component perpendicular to the surface of the semiconductor substrate. It should be noted that the magnetic field component perpendicular to the surface of the semiconductor substrate is detrimental to inducing in-plane uniaxial magnetic anisotropy and will reduce the rate of epitaxial growth of the magnetic layer of gyromagnetic ferrite.
[0086] The process of growing a magnetic layer of gyromagnetic ferrite is illustrated below with a specific example:
[0087] A C-shaped electromagnet outside the reaction chamber generates a magnetic field parallel to the surface of the semiconductor substrate. The magnetic field strength can be adjusted from 0 to 0.3 T, and the magnetic field uniformity within the semiconductor substrate range is better than 90%.
[0088] The GaAs substrate was placed in the reaction chamber and heated to the growth temperature of 600℃~700℃. A metal-organic source precursor gas of yttrium (Y), thulium (Tm), and iron (Fe), along with oxygen, was introduced to begin Tm doping. 3+ The epitaxial growth of YIG thin films, specifically Tm:YIG thin films. The precursor gas for Y is C. 15 H 15 The precursor gas for Y and Fe is C a H b FeO c The precursor gas for Tm can be tris(cyclopentadienyl)thulium(III)C 15 H 15 Tm.
[0089] Simultaneously, a magnetic field of 0.2 T parallel to the substrate surface is applied using a C-shaped electromagnet. The substrate rotates at 20 rpm to ensure uniform growth of the Tm:YIG thin film.
[0090] X-ray diffraction (Φ-scan) revealed that the Tm:YIG thin film grown in this example exhibits a strong in-plane texture. Vibrating sample magnetometer tests showed that the easy magnetization axis of the Tm:YIG thin film is parallel to the direction of the magnetic field applied during growth, demonstrating significant in-plane uniaxial magnetic anisotropy. However, if no magnetic field is applied during the growth of the Tm:YIG thin film, the resulting Tm:YIG thin film has an in-plane polycrystalline structure and is magnetically isotropic, with no obvious easy magnetization direction.
[0091] It should be noted that after growing the magnetic layer of the gyromagnetic ferrite, the variable temperature annealing process in step S102 is performed to forcibly change its easy magnetization axis from parallel to the semiconductor substrate surface to perpendicular to the semiconductor substrate surface.
[0092] The magnetic layer of the gyromagnetic ferrite mass-produced using the MOCVD process disclosed in this embodiment can be integrated with standard semiconductor processes, such as photomasks and photolithography, to mass-produce circuit patterns with complex shapes.
[0093] An exemplary embodiment of this disclosure provides an epitaxial structure prepared using the above-described preparation method. The magnetic layer in the epitaxial structure of this embodiment has a low saturation magnetization, thus requiring little or no external excitation of the magnetic field during application.
[0094] In some examples, the epitaxial structure includes a semiconductor substrate and a magnetic layer of gyromagnetic ferrite epitaxially grown on the semiconductor substrate. The magnetic layer of gyromagnetic ferrite exhibits perpendicular magnetic anisotropy, and its easy magnetization axis is perpendicular to the surface of the semiconductor substrate. This example of the epitaxial structure can be used to fabricate microwave devices such as microwave filters, microwave oscillators, microwave circulators, and microwave isolators, and is widely used in communication and radar systems. This example of the epitaxial structure can also be used to fabricate magneto-optical devices such as optical isolators, magneto-optical circulators, and magneto-optical modulators, and is widely used in fiber optic communication and laser systems. The near-single-crystal high-quality gyromagnetic ferrite magnetic layer in the epitaxial structure can effectively reduce the insertion loss of microwave or magneto-optical devices.
[0095] An exemplary embodiment of this disclosure provides a semiconductor device including the epitaxial structure described above. In some examples, the semiconductor device is a microwave device or a magneto-optical device. The semiconductor device provided in this embodiment has advantages such as high integration, high performance, and high reliability.
[0096] Among them, a microwave circulator is a multi-port non-reciprocal device that can transmit electromagnetic waves or optical signals in a fixed order from one port to the next, while preventing reverse transmission. Figure 6 This is a schematic diagram illustrating the structure of a microwave circulator. For example... Figure 6 As shown, the microwave circulator based on YIG thin film has a sandwich-like layered structure with a central Y-branch conductor, typically made of copper (Cu). The three ports of the Y-branch are port 1, port 2, and port 3. On either side of the central conductor are, in sequence, a ferromagnetic material, a uniform magnetic sheet, and a permanent magnet. The ferromagnetic material is a YIG ferromagnetic material, used to rotate the polarization direction of the electromagnetic wave propagating in the Y-branch conductor. When an electron wave is input to port 1, the YIG ferromagnetic material rotates the polarization direction of the electromagnetic wave in the Y-branch. This results in the electromagnetic wave in port 2 being resonantly reinforced, while the electromagnetic wave in port 3 is resonantly canceled. Therefore, the electromagnetic wave input to port 1 can only be output from port 2 and cannot be output through port 3, thus forming the microwave circulator.
[0097] It should be noted that when an absorption resistor is connected to port 3, the electromagnetic wave output from port 1 can be output from port 2, while the electromagnetic wave input from port 2 loops to port 3 and is absorbed by the resistor, forming a microwave isolator. To increase the isolation between ports, microwave circulators and microwave isolators can be cascaded.
[0098] In such Figure 6 In the microwave circulator shown, a permanent magnet excites a ferromagnetic material, generating a gyromagnetic effect. The magnetic field of the permanent magnet is fixed, therefore the change in the polarization direction of the electromagnetic wave propagating in the Y-branch conductor by the ferromagnetic material is also fixed. If the excitation magnet is replaced with a coil electromagnet, the ferromagnetic material can be excited in both forward and reverse directions by switching the direction of the current in the electromagnet. The polarization direction of the electromagnetic wave in the Y-branch conductor can be either forward or reverse. When the parameters are properly matched, the gyromagnetic effect generated by the excited ferromagnetic material when a forward current is applied causes the electromagnetic wave to be output from port 2, while the forward and reverse electromagnetic waves cancel each other out at port 3, resulting in no output. Conversely, when a reverse current is applied, the electromagnetic wave is output from port 3, and there is no output from port 2. This forms a single-pole double-throw microwave switch. Compared with solid-state switching elements, the main advantages of ferrite switches are low insertion loss, high power capacity, and a switching time on the order of microseconds.
[0099] When different channels of a microwave switch are connected to different phase-shifting devices, a phase shifter is formed. When a microwave switch is combined with a variable power divider (VPD), a phase and amplitude controller (PAC), and a phase shifter, a programmable beamforming network (BFN) is formed. A programmable BFN can be used to shape antenna radiation, enabling UHF multi-beam antennas to transmit and receive signals, which is of great significance for next-generation Ku / Ka and other high-frequency satellite communications.
[0100] In addition, YIG single crystals have very low microwave losses, and YIG single crystal spheres or disks used as resonators have very high Q values. When the magnetic field generated by the external current coil changes, the resonant frequency of the YIG modulator also changes, making it suitable for use as an electrically tunable filter, primarily in electronic countermeasures and microwave instruments.
[0101] While specific embodiments of this disclosure have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of this disclosure is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of this disclosure, but all such changes and modifications fall within the scope of protection of this disclosure.
Claims
1. A method for preparing an epitaxial structure, characterized in that, Includes the following steps: In the reaction chamber, a magnetic layer of gyromagnetic ferrite is epitaxially grown on a semiconductor substrate; wherein the magnetic layer of gyromagnetic ferrite has in-plane uniaxial magnetic anisotropy, and the easy magnetization axis is parallel to the surface of the semiconductor substrate. The semiconductor substrate is placed in an annealing chamber for variable temperature annealing, and a magnetic field perpendicular to the surface of the semiconductor substrate is applied in the annealing chamber to forcibly change the easy magnetization axis from parallel to the substrate surface to perpendicular to the substrate surface; wherein, the variable temperature annealing process is to subject the semiconductor substrate to at least one temperature change process between a first temperature and a second temperature, wherein the first temperature is higher than the second temperature.
2. The preparation method according to claim 1, characterized in that, The second temperature is lower than the Curie temperature of the magnetic layer, and the preparation method further includes: In response to the semiconductor substrate cooling to below a third temperature, the application of the magnetic field in the annealing chamber is stopped; wherein the third temperature is lower than the Curie temperature and higher than the second temperature.
3. The preparation method according to claim 1, characterized in that, The semiconductor substrate undergoes the temperature change process 2 to 20 times.
4. The preparation method according to claim 1, characterized in that, The first temperature is 50°C to 100°C higher than the growth temperature of the magnetic layer, and / or the second temperature is 100°C to 200°C lower than the growth temperature of the magnetic layer.
5. The preparation method according to claim 1, characterized in that, The step of placing the semiconductor substrate in an annealing chamber for variable-temperature annealing specifically includes: The semiconductor substrate is automatically transferred from the reaction chamber to the annealing chamber for variable temperature annealing.
6. The preparation method according to claim 1, characterized in that, The strength of the magnetic field applied in the annealing chamber ranges from 1T to 1.5T.
7. The preparation method according to any one of claims 1-6, characterized in that, The gyromagnetic ferrite is yttrium iron garnet ferrite.
8. An epitaxial structure, characterized in that, The epitaxial structure is prepared by the preparation method according to any one of claims 1-7.
9. An epitaxial structure, characterized in that, include: Semiconductor substrate; as well as A magnetic layer of gyromagnetic ferrite epitaxially grown on the semiconductor substrate; The magnetic layer of the gyromagnetic ferrite has perpendicular magnetic anisotropy, and its easy magnetization axis is perpendicular to the surface of the semiconductor substrate.
10. A semiconductor device, characterized in that, Includes the epitaxial structure as described in claim 8 or 9.