A semiconductor / metal / semiconductor quantum well structure, preparation method and application thereof
By using the two-step method to grow Al film on the Si substrate, the problem of high-quality single crystal Al film is solved, and the high-quality Si/Al/Si structure is achieved, which improves device performance and qubit life.
Patent Information
- Application Number
- CN202111211968.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-10-18
- Publication Date
- 2025-08-26
- Estimated Expiration
- 2041-10-18
AI Technical Summary
The prior art is difficult to efficiently grow high-quality single crystal Al films, especially on Si substrates, resulting in limited device performance and difficulty in achieving high-quality Si/Al/Si sandwich structures and semiconductor/metal/semiconductor epitaxial structures.
The Al film was grown on the Si substrate by a two-step method, first growing the Al seed layer at -50°C-50°C, then annealing at 100°C-200°C, and then growing the metal Al film layer at 50°C-200°C, and annealing at 100°C-500°C to form a high-quality single crystal Al film.
A high-quality Al film with flat surface and no twins is obtained, which reduces interface losses and improves device performance, especially in superconducting quantum computing and microwave circuits, which extends the coherence time of qubits and reduces microwave losses.
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Figure CN113972319B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for obtaining a high-quality wafer-sized Al single crystal film and a semiconductor / metal / semiconductor quantum well structure containing the single crystal Al film, an epitaxial preparation method and applications thereof. More specifically, the present invention relates to the optimization of conditions for direct epitaxial high-quality Al growth on a Si substrate, including substrate processing, optimization of the Al growth temperature and an in-situ annealing process. Background Art
[0002] Metallic aluminum thin films, with their excellent barrier and corrosion resistance, good electrical conductivity and optical properties, and their positive economic significance, play a crucial role in the design of various multilayer, highly reflective films and thin-film devices. Al films with a purity greater than 99.95% resist corrosion from most acids and can be used as protective films for instruments. Metallic aluminum thin films, with excellent electrical conductivity second only to silver and copper, are widely used in electrical devices and electrode fabrication. In particular, in the fabrication of plasmonic optoelectronic devices, metallic aluminum thin films can serve as substrates for direct epitaxial growth of device structures.
[0003] With technological advancements, device applications are placing increasingly stringent demands on metal thin films for purity, crystal quality, and surface flatness. However, many current preparation methods for metal thin films no longer meet these requirements. Molecular beam epitaxy (MBE) enables precise atomic-level control, resulting in high-quality, single-crystalline Al thin films with smooth surfaces. Efficient integration of metals and semiconductors is also crucial in CMOS processes. Interface manipulation of Al / Si, a classic metal-semiconductor contact structure, plays a significant role in the growth of high-quality Al thin films. Although the lattice constants of Al and Si differ significantly (the lattice mismatch is 33.9%), four Al lattices correspond to three Si lattices, significantly reducing the lattice mismatch between Al and Si to 0.47%. Current Al thin film growth methods generally operate at or below room temperature. Al films grown on untreated Si substrates are typically polycrystalline, exhibit numerous twins, and exhibit significant surface roughness. The commonly used epitaxial growth method for single-crystal Al is to process the Si (111) substrate into a 7×7 reconstructed surface, and then perform low-temperature growth directly on the 7×7 surface. The surface of the grown Al film is smooth but is usually accompanied by the formation of twins. The twin boundaries will cause certain losses in the application of high-performance devices. Although there are reports that the quality of Al films grown on √3×√3 reconstructed surfaces can be further improved, the acquisition of this reconstructed surface is relatively complex and the entire process takes a long time (more than 5-6 hours). Therefore, it is very necessary to seek a simple and efficient method for growing single-crystal Al.
[0004] High-quality single-crystalline Al thin films are attracting increasing attention for their applications in ultraviolet plasmonics and superconducting quantum computing. The crystal quality and surface flatness of Al thin films play a crucial role in the performance of these devices. For example, surface inhomogeneity and grain boundary disorder can lead to scattering losses of surface plasmons, thereby limiting the performance of plasmon devices. Furthermore, in superconducting quantum computing devices, the main factors affecting the coherence time of qubits are the amorphous layer at the surface interface during qubit fabrication and the two-level defects formed by the adsorption of molecular functional groups during device fabrication. To improve the lifetime of superconducting qubits, it is necessary to fundamentally reduce the amount of amorphous material in the chip fabrication process and avoid the introduction of surface and interface impurities. High-quality Al thin films can reduce microwave losses, improve the quality factor of the resonant cavity, and increase the coherence time of qubits. Research on the integration of high-quality single-crystalline Al with Si is also of great significance in CMOS processes.
[0005] Based on high-quality single-crystal Al thin films, high-quality Si / Al / Si sandwich structures can be further realized. The new physical effects that appear in such semiconductor / metal / semiconductor structures will lead to improved performance of related devices and even give birth to new electronic devices. Taking superconducting quantum computing as an example, compared with the traditional Nb / AlO-based x / Nb or Al / AlO x The Josephson junction of a Si / Al structure and a Si / Al / Si structure exhibit both superconducting and semiconducting properties. Al can serve as a delta-doping layer in the Si / Al / Si structure, and theoretical predictions indicate superconductivity. Si atoms, due to their small order number and large band gap, exhibit low spin-orbit coupling, allowing them to maintain a long coherence time during spin relaxation. Furthermore, the Si / Al / Si structure can be precisely manipulated through molecular beam epitaxy, significantly reducing interface losses. This structure holds great potential for application in Group IV semiconductor quantum information processing devices. Furthermore, semiconductor / metal / semiconductor transistors have long been a desired device in microwave circuit design, but this has been hindered by the difficulty of obtaining high-quality semiconductor / metal / semiconductor epitaxial structures, particularly high-quality semiconductor epitaxy on metal. High-quality Al thin film growth technology can improve the quality of semiconductor epitaxy on Al, thereby enabling the realization of high-quality Si / Al / Si sandwich structures. In addition, in the Si / Al / Si sandwich structure, the energy band can be controlled by regulating the thickness of the Al layer to obtain a Si / Al / Si quantum well structure. The success of the sandwich structure can also further realize the Si / Al superlattice structure. Combined with the doped semiconductor layer, more new transistor structures can be realized, opening up new avenues for the development of microwave electronic devices. Summary of the Invention
[0006] In order to achieve the above-mentioned purpose of the invention, the present invention provides a semiconductor / metal / semiconductor quantum well structure, characterized in that it includes a first semiconductor layer, a metal Al thin film layer and a second semiconductor layer, wherein the metal Al thin film layer is sandwiched between the first semiconductor layer and the second semiconductor layer, and the metal Al thin film layer is a single crystal with a unique orientation and has no twins.
[0007] In a preferred embodiment of the present invention, the thickness of the metal Al thin film layer is 0.1-100 nm.
[0008] In a preferred embodiment of the present invention, the first semiconductor layer is a single crystal layer.
[0009] In a preferred embodiment of the present invention, the first semiconductor layer and / or the second semiconductor layer is a doped semiconductor.
[0010] The present invention also provides a method for preparing a semiconductor / metal / semiconductor quantum well structure, which specifically comprises the following steps:
[0011] (1) First, pre-treating the first semiconductor layer;
[0012] (2) growing an Al seed layer on the first semiconductor layer at -50°C to 50°C by epitaxial growth;
[0013] (3) heating the Al seed layer for annealing;
[0014] (4) Growing a metal Al thin film layer by epitaxial method;
[0015] (5) Growing a second semiconductor layer by epitaxial growth to obtain a semiconductor / metal / semiconductor quantum well structure;
[0016] (6) Heating the semiconductor / metal / semiconductor quantum well structure for annealing.
[0017] In a preferred embodiment of the present invention, the pretreatment method includes a chemical method and a thermal treatment method.
[0018] In a preferred embodiment of the present invention, the annealing temperature in step (3) is 100°C-200°C, and the annealing time is 10-30 minutes.
[0019] In a preferred embodiment of the present invention, the growth temperature in step (4) is 50°C-200°C, and the growth rate is 0.1-1 nm / min.
[0020] In a preferred embodiment of the present invention, the annealing temperature in step (6) is 100°C-500°C, and the annealing time is 10-30 minutes.
[0021] In a preferred embodiment of the present invention, after step (1), a homogeneous buffer layer is first grown.
[0022] The present invention also provides a semiconductor quantum information device, comprising the above-mentioned semiconductor / metal / semiconductor quantum well structure.
[0023] The present invention uses a two-step method of first growing an Al seed layer and then growing an Al thin film layer to epitaxially grow high-quality Al single crystal thin films and semiconductor / metal / semiconductor quantum well structures on a semiconductor substrate, providing an optimized preparation method and having the following advantages over existing technologies:
[0024] (1) The Al film prepared by the method of the present invention has a smooth surface with a roughness of 100-200 μm, high single crystal quality, and no twins;
[0025] (2) The present invention grows the Al seed layer at low temperature (-50-50°C) to ensure a smooth interface and surface;
[0026] (3) The present invention performs in-situ annealing of the Al seed layer obtained at low temperature at 100-200°C, which can eliminate twins and further improve crystal quality;
[0027] (4) The present invention continues to carry out homoepitaxial growth of Al at 100°C to ensure high-quality Al single crystal thin films;
[0028] (5) The optical loss of the Al film grown by the present invention is 50% or less than that of conventional Al films, which further verifies the crystal quality of the Al seed layer and ensures the quality of the subsequently grown Al / Si interface and Si layer;
[0029] (6) The thermal conductivity of the Al / Si heterojunction interface in the Si / Al / Si quantum well grown by the present invention reaches 0.5 GW m at room temperature. -2 K -1 This is the highest value reported so far;
[0030] (7) The present invention grows a semiconductor / metal / semiconductor quantum well structure, which has both superconducting and semiconductor properties. Low-temperature molecular beam epitaxy reduces the influence of Al diffusion in Si, and holes are confined in the quantum well. In addition, the Al layer buried in Si can reduce environmental noise and can be used in semiconductor quantum information devices. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The invention may be better understood by reference to the accompanying drawings which illustrate embodiments of the invention, in which:
[0032] Figure 1 is a schematic diagram of the semiconductor / metal / semiconductor quantum well structure of the present invention;
[0033] Figure 2It is a structural schematic diagram and an equivalent circuit diagram of the semiconductor quantum information device of the present invention;
[0034] Figure 3 is the AFM morphology of the 10 nm Al film surface under different conditions;
[0035] Figure 4 The AFM morphology of the 80 nm Al film surface under different conditions;
[0036] Figure 5 Shown with Figure 4 Corresponding series of 80nm Al thin films (a) X-ray diffraction 2θ-ω scans; (b) X-ray diffraction phi scans;
[0037] Figure 6 The comparison of the optical dielectric constants of Al films grown directly at low temperature (-50-50°C) and Al films grown using a two-step method;
[0038] Figure 7 This is a scanning transmission electron microscope image of Al thin film grown by two-step method. DETAILED DESCRIPTION
[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0040] The present invention provides a semiconductor / metal / semiconductor quantum well structure, such as Figure 1 As shown, it includes a first semiconductor layer 1, a metal Al thin film layer 2 and a second semiconductor layer 3, wherein the metal Al thin film layer 2 is sandwiched between the first semiconductor layer 1 and the second semiconductor layer 3, wherein the metal Al thin film layer 2 is a single crystal with a unique orientation and no twins. This structure obtains a semiconductor / metal / semiconductor quantum well system by burying a single crystal Al layer in Si, thereby forming a perfect ohmic contact between the metal region and the semiconductor region, without the presence of a Schottky barrier, and almost no interface state between the metal region and the semiconductor region, which can reduce interface losses in the application of semiconductor quantum devices, thereby increasing the lifetime of quantum bits. At the same time, in the application of surface plasmons, surface inhomogeneity and disordered grain boundaries can lead to scattering losses of surface plasmons, while single crystal and twin-free metal films can reduce the losses caused by grain boundaries. The thickness of the metal Al thin film layer is 0.1-100nm.
[0041] The first semiconductor layer and the second semiconductor layer are commonly used semiconductor materials, such as Si, Ge, GaAs, AlGaAs, etc. The first semiconductor layer can be a single crystal layer, which can further improve the surface flatness, thereby improving the surface flatness of the subsequent metal Al thin film growth. The first semiconductor layer and / or the second semiconductor layer can be a doped semiconductor, and the doping source can be a commonly used doping source. Taking Si as an example, n-type doping sources include but are not limited to S, P, As, and p-type doping sources include but are not limited to B and Ga. The main effect of doping is to regulate the Fermi level of the semiconductor and thus change the band alignment between the metal and the semiconductor. The band alignment method can change the contact resistance and contact thermal resistance of the metal / semiconductor interface.
[0042] The present invention provides a method for preparing a semiconductor / metal / semiconductor quantum well structure by epitaxy, by growing an Al single crystal thin film on a semiconductor substrate and improving its crystal quality through a two-step process. The specific preparation method is as follows:
[0043] (1) First, pre-treating the first semiconductor layer;
[0044] (2) growing an Al seed layer on the first semiconductor layer by an epitaxial method at a temperature of -50°C to 50°C;
[0045] (3) heating the Al seed layer for annealing;
[0046] (4) Growing a metal Al thin film layer by epitaxial method;
[0047] (5) Growing a second semiconductor layer by epitaxial growth to obtain a semiconductor / metal / semiconductor quantum well structure;
[0048] (6) Heating the semiconductor / metal / semiconductor quantum well structure for annealing.
[0049] This preparation method can precisely control the thickness of the metal Al thin film layer and the semiconductor layer. At the same time, the structure forms a semiconductor / metal / semiconductor quantum well system by burying the Al layer in the semiconductor layer. This structure forms a perfect ohmic contact between the metal region and the semiconductor region, without the presence of a Schottky barrier and no interface state between the metal region and the semiconductor region. It is expected to reduce interface losses in the application of semiconductor quantum devices, thereby increasing the lifetime of quantum bits. In addition, the structure can be prepared by epitaxial growth to further realize a semiconductor / Al superlattice structure, or combined with a doped semiconductor layer to obtain a more flexible transistor structure, opening up new avenues for realizing new transistor mechanisms. At the same time, the two-step method of first growing a seed layer and then growing a thin film layer can eliminate twins and further improve crystal quality.
[0050] Preferably, after step (1), a homogeneous buffer layer can be grown first. The homogeneous buffer layer can improve the surface flatness to a certain extent, thereby improving the surface flatness of subsequent thin film growth. The pretreatment method in step (1) includes a chemical method and a heat treatment method. The annealing temperature in step (3) is 100°C-200°C, and the annealing time is 10-30 minutes. By controlling the annealing temperature and time, the crystal quality of Al can be improved and twins can be eliminated. The growth temperature in step (4) is 50°C-200°C, and the growth rate is 0.1-1 nm / min. At the same time, the semiconductor layer grown in step (5) can be N-type doped or P-type doped, and the selected doping source is a commonly used doping source for the semiconductor material. The annealing temperature in step (6) is 100°C-500°C, and the annealing time is 10-30 minutes, which can further improve the quality of the crystal and the entire semiconductor / metal / semiconductor quantum well structure.
[0051] In the embodiment of the present invention, the first semiconductor layer is made of a Si single crystal substrate.
[0052] The present invention also provides a semiconductor quantum information device, which includes the above-mentioned semiconductor / metal / semiconductor quantum well structure. Compared with the traditional semiconductor quantum well structure, the narrow bandgap semiconductor is replaced by metal, which has a continuous electronic state density and can achieve a faster device response speed. By regulating the doping of the semiconductor (Si) layer in the quantum well structure, a perfect ohmic contact can be formed between the metal region and the semiconductor region, and a Schottky barrier can also be formed; by regulating the thickness of the metal layer, the tunneling current of the semiconductor / metal / semiconductor quantum well can be controlled; and by etching, a portion of the metal Al thin film layer can be exposed, such as Figure 2 As shown, electrodes are connected to the two Si and Al layers respectively, and the equivalent circuit is equivalent to two Schottky diodes connected in reverse series, which can be used in microwave circuits; when the thickness of the Al layer is very thin, precise interface control is performed through the epitaxial method to eliminate the possible interface states between the metal region and the semiconductor region, greatly reducing the contact resistance and contact thermal resistance, thereby reducing interface losses, which can be used for superconducting quantum computing. Example
[0053] First, the (111) crystal plane Si substrate is deoxidized and treated with 8% hydrofluoric acid for 1 minute to form a hydrogen-passivated surface. The substrate is then placed in a Group IV molecular beam epitaxy (MBE) apparatus and dehydrogenated at 900-1000°C to obtain a clean Si surface. A Si buffer layer can be grown on the Si surface, which can improve surface flatness to a certain extent, thereby improving the surface flatness of subsequent thin film growth.
[0054] Next, an Al seed layer is grown at -50°C to 50°C. The low-temperature growth and high-temperature annealing of the seed layer can produce high-quality Al single crystals, which serve as a template for subsequent epitaxial growth, ensuring the quality of subsequent epitaxy.
[0055] The Al seed layer is heated to 100° C.-200° C. and annealed for 10-30 minutes.
[0056] Then, a 0.1-100 nm thick Al film is grown at a growth temperature of 50°C-200°C.
[0057] A Si film is grown on the Al layer by molecular beam epitaxy to obtain a Si / Al / Si heterostructure. The Si / Al / Si quantum well structure is then heated to 100-500°C and annealed for 10-30 minutes.
[0058] Figure 3 The AFM images of (a) an Al film epitaxially grown on a Si (7×7) reconstructed surface with a growth temperature of 0°C and a thickness of 10 nm are shown. (b) The growth conditions and thickness are the same as (a), but after in-situ annealing at 100°C, it can be seen that a smooth Al film can be obtained under these growth conditions and that annealing has no significant effect on the surface morphology and roughness.
[0059] Figure 4 AFM of an 80nm thick Al film is shown. The growth conditions are as follows:
[0060] (Ref.) Al film epitaxially grown directly on the non-dehydrogenated substrate surface, i.e., Si (1×1) reconstructed surface, at a growth temperature of 0°C was used as a reference;
[0061] (A) Direct epitaxial growth of Al thin film on Si (7×7) reconstructed surface at a growth temperature of 0°C.
[0062] (B) AFM image of the Al film grown by the two-step method of the present invention. It can be seen that the Al film obtained by the two-step method has a smoother surface.
[0063] Figure 5 Shown is the Figure 3 Corresponding 80nm Al film (a) X-ray diffraction 2θ-ω scan; (b) X-ray diffraction phi scan. It can be seen that the reference sample Al film has different crystal orientations Al (111) and Al (200), and the phi scan shows a higher twin ratio. A is Figure 3 (a) corresponds to the sample with a smaller twin ratio. Figure 3(b) The corresponding sample has no twin peak, and the Al (111) peak has a narrower half-height width from the X-ray diffraction scan, indicating that sample B, that is, the Al film grown by the two-step method used in the present invention, has higher crystal quality and can effectively inhibit the formation of twins.
[0064] Figure 6 Comparison of the optical dielectric constant ε² of Al films grown directly at 0°C (A) and using a two-step method (B), as well as a comparison with the Palik reference value. Compared to the Palik reference value, the Al films grown using the two-step method of the present invention exhibit significantly lower optical loss across all wavelengths, with ε² reduced by 40% in the UV band. Optical loss in the UV and visible bands is also reduced compared to conventional Al films grown directly at low temperatures, further demonstrating the high crystal quality of the Al films grown using the present invention.
[0065] Figure 7 This is an atomically resolved scanning transmission electron micrograph of an Al thin film grown via a two-step process. It shows the Al / Si interface along the
[110] direction. The interface is sharp and clear, with five Al atoms for every four Si atoms, resulting in a minimal Al / Si mismatch. The inset is a Fast Fourier Transform (FFT) diffraction pattern of the Al lattice, demonstrating the high-quality single-crystalline nature of the Al.
[0066] Based on the above characterizations, it can be seen that the present invention uses a two-step method to grow high-quality Al single crystal thin films on Si substrates at low temperature with a smooth surface and high single crystal quality, which provides application prospects for Si / Al / Si in semiconductor quantum devices.
Claims
1. A semiconductor / metal / semiconductor quantum well structure, characterized in that: It includes a first semiconductor layer, a metal Al thin film layer and a second semiconductor layer, wherein the metal Al thin film layer is sandwiched between the first semiconductor layer and the second semiconductor layer, the metal Al thin film layer is a single crystal with a unique orientation and no twins, and the thickness of the metal Al thin film layer is 0.1-100nm.
2. The semiconductor / metal / semiconductor quantum well structure according to claim 1, characterized in that: The first semiconductor layer is a single crystal layer.
3. The semiconductor / metal / semiconductor quantum well structure according to claim 1, characterized in that: The first semiconductor layer and / or the second semiconductor layer is a doped semiconductor.
4. A method for preparing a semiconductor / metal / semiconductor quantum well structure, characterized in that: include: (1) First, pre-treating the first semiconductor layer; (2) growing an Al seed layer on the first semiconductor layer by an epitaxial method at a temperature of -50°C to 50°C; (3) heating the Al seed layer for annealing; (4) Growing a metal Al thin film layer by epitaxial method; (5) Growing a second semiconductor layer by epitaxial growth to obtain a semiconductor / metal / semiconductor quantum well structure; (6) Heating the semiconductor / metal / semiconductor quantum well structure for annealing.
5. The preparation method according to claim 4, characterized in that The pretreatment methods include chemical methods and thermal treatment methods.
6. The preparation method according to claim 4, characterized in that In step (3), the annealing temperature is 100°C-200°C, and the annealing time is 10-30 minutes.
7. The preparation method according to claim 4, wherein In step (4), the growth temperature is 50°C-200°C, and the growth rate is 0.1-1 nm / min.
8. The preparation method according to claim 4, characterized in that In step (6), the annealing temperature is between 100°C and 500°C, and the annealing time is between 10 and 30 minutes.
9. The preparation method according to claim 4, characterized in that After step (1), a homogeneous buffer layer is first grown.
10. A semiconductor quantum information device, characterized in that: The semiconductor / metal / semiconductor quantum well structure comprises the semiconductor / metal / semiconductor quantum well structure according to any one of claims 1 to 3.