A method for preparing a wafer-level self-supporting CdTe thin film

Abstract

The application discloses a preparation method of a wafer-level self-supporting CdTe film, and comprises the following steps: providing a two-dimensional material / sapphire substrate; growing a CdTe film on the surface of the two-dimensional material / sapphire substrate; separating the CdTe / two-dimensional material from the surface of the sapphire substrate by a heat-releasing tape peeling method; and removing the viscosity of the heat-releasing tape by heating to obtain a high-quality self-supporting CdTe film. The method utilizes the good lattice matching between the sapphire substrate and the CdTe film, and utilizes the two-dimensional material as a transition layer to avoid the bonding of the dangling bonds on the surface of the sapphire and the CdTe film. The CdTe film is grown by a molecular beam epitaxy system, the CdTe film is peeled from the substrate by using the heat-releasing tape, and finally the viscosity of the tape is removed by heating to obtain the self-supporting CdTe film. The self-supporting CdTe film prepared by the application can be widely compatible with silicon-based electronic devices, and has great application value in flexible wearable electronic devices and the like.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic semiconductor thin film manufacturing, specifically a method for preparing wafer-level self-supporting CdTe thin films. Background Technology

[0002] CdTe is a cubic zincblende semiconductor. CdTe thin films are generally prepared by epitaxial growth on traditional substrate materials. The first method involves epitaxially growing CdTe along the same crystal direction on cubic crystals with significant lattice mismatch, such as silicon, germanium, and gallium arsenide. However, due to the large lattice mismatch between these substrates, severe lattice distortion occurs at the interface, resulting in numerous dislocations, stacking faults, and other defects in the CdTe thin films, severely affecting the film's crystal quality. The second method involves epitaxially growing CdTe along the diagonal of the cubic unit cell on a hexagonal sapphire substrate. CdTe grown along this direction has a similar in-plane lattice constant to the sapphire substrate, resulting in relatively better quality CdTe thin films. However, CdTe thin films grown directly on sapphire substrates are difficult to integrate with current mainstream silicon-based integrated circuit processes. Furthermore, strong forces exist between the substrate and the CdTe thin film, making it difficult to transfer and integrate CdTe thin films into silicon-based electronic devices. This limits its application in the semiconductor field, thus necessitating the design of new fabrication methods. Summary of the Invention

[0003] The purpose of this invention is to provide a wafer-level self-supporting CdTe thin film preparation method to address the shortcomings of existing technologies. This method epitaxially grows a CdTe thin film on a two-dimensional material / sapphire substrate, exhibiting good crystal quality and continuity. Utilizing the weak van der Waals forces between the two-dimensional material and the sapphire substrate, the self-supporting CdTe thin film can be freely transferred to any substrate via a peel-and-thermal release method. This solves the problem of poor compatibility between high-quality CdTe thin films and silicon-based electronic devices and is widely applicable to other flexible electronic devices.

[0004] Specific technical solutions for achieving the objectives of this invention:

[0005] A method for preparing a wafer-level self-supporting CdTe thin film includes the following steps: selecting a suitable two-dimensional material / sapphire substrate and pre-treating it to obtain a clean surface; assembling the pre-treated substrate and transferring it to a molecular beam epitaxy system; controlling the molecular beam epitaxy process to epitaxially grow a CdTe thin film on the two-dimensional material / sapphire substrate; and obtaining the wafer-level self-supporting CdTe thin film by a peel-and-heat release method.

[0006] The two-dimensional material is one of graphene, molybdenum disulfide, and molybdenum ditelluride; the two-dimensional material has a single-layer structure.

[0007] The pretreatment to obtain a clean surface is achieved by cleaning the two-dimensional material / sapphire substrate with acetone, anhydrous ethanol, and deionized water, followed by heating at 100°C for 60 minutes under a nitrogen atmosphere.

[0008] The substrate assembly involves welding a two-dimensional material / sapphire substrate and a substrate heating support together using molten metal, wherein the molten metal is indium or a lead-tin alloy.

[0009] The CdTe thin film is prepared by molecular beam epitaxy, wherein: the beam source of molecular beam epitaxy adopts CdTe and Te sources with a purity of 7N or higher, the equivalent pressure ratio of the beam current is controlled to CdTe∶Te=1∶0.5~0.7, the temperature of the heating wire in the molecular beam epitaxy system is controlled to be 280~320℃, the growth time is controlled to be between 10-90min, the thickness of the epitaxially grown CdTe thin film is 50-500nm, the out-of-plane crystal orientation of the film is along the

[111] direction, and the film size is 0.5cm×0.5cm~1cm×1cm.

[0010] The peel-and-release process involves peeling the epitaxially grown CdTe film from the two-dimensional material / sapphire substrate using a heat-release adhesive tape, and then removing the tape by heating to transfer the CdTe film to any substrate, thus obtaining a self-supporting CdTe film. Specifically, the heat-release adhesive tape is polydimethylsiloxane, and the temperature for removing the tape is set to 90-110°C, with a heating time of 3-5 minutes.

[0011] The CdTe thin film growth method provided by this invention utilizes the matching lattice constant between CdTe and sapphire substrate to facilitate CdTe nucleation on the substrate. Then, the weak van der Waals forces on the surface of the two-dimensional material are used to isolate the strong interaction forces between CdTe and sapphire substrate. Finally, a high-quality, continuous, self-supporting CdTe thin film is obtained on the two-dimensional material / sapphire substrate. This CdTe thin film can be transferred to any substrate by peel-heat release transfer.

[0012] Compared with existing technologies, the CdTe thin films obtained by this invention have the characteristics of high quality and large-area continuity. They can be separated from the original substrate and transferred to any other substrate, making them compatible with mainstream silicon-based integrated circuits. This solves the problems of large defects and poor quality of heteroepitaxial CdTe thin films on silicon substrates. Attached Figure Description

[0013] Figure 1 A flowchart illustrating the preparation process of the self-supporting CdTe thin film provided by this invention;

[0014] Figure 2 A physical image of the wafer-level self-supporting CdTe thin film prepared according to the present invention;

[0015] Figure 3 A scanning electron microscope image of the wafer-level self-supporting CdTe thin film prepared in this invention;

[0016] Figure 4 High-resolution X-ray diffraction patterns of the wafer-level self-supporting CdTe thin film prepared for this invention on a sapphire substrate and after being transferred to a silicon substrate via peel-and-thermal release. Detailed Implementation

[0017] To clarify the objectives and technical advantages of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are merely specific embodiments of this invention, and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are all within the protection scope of this invention. Example

[0018] This invention provides a method for fabricating wafer-level self-supporting CdTe thin films, combined with... Figure 1 As shown, it includes the following steps:

[0019] Step 1: Provide a two-dimensional material / sapphire substrate and clean it to obtain a clean surface. Specifically, rinse the surface of the two-dimensional material 1 / sapphire substrate 2 thoroughly with acetone, anhydrous ethanol and deionized water respectively, and then bake it at 100°C for 60 minutes in a nitrogen-protected atmosphere to remove surface moisture.

[0020] Step 2: Assemble the two-dimensional material 1 / sapphire substrate 2 and the substrate heating bracket. Specifically, first heat the substrate heating bracket to approximately 180°C. Then, place 0.2g of indium or lead-tin alloy on the surface of the substrate heating bracket. After the metal has completely melted, use a tungsten sheet to evenly coat the molten metal. Next, move the sapphire side of the substrate onto the molten metal, repeatedly pushing and pulling to ensure full contact between the substrate and the molten metal. Turn off the heating temperature; the assembly is now complete.

[0021] Step 3: Perform vacuum pretreatment on the two-dimensional material 1 / sapphire substrate 2. Specifically, the assembled substrate and heating support are transferred to the pretreatment chamber of the molecular beam epitaxy system, where a vacuum of 10... -9 The substrate is heated to 200°C under Torr conditions for 120 minutes to remove impurity molecules adsorbed on the surface during substrate transport.

[0022] Step 4: Epitaxial growth of self-supporting CdTe thin film 3. Specifically, the substrate is transferred to the growth chamber of the molecular beam epitaxy system and heated to 280℃~320℃. The mechanical motor is turned on to rotate the substrate heating support at a constant speed of 0.1 r / s. The crucibles containing CdTe and Te sources are then heated separately. By controlling the crucible heating temperature, the beam equivalent pressure ratio CdTe∶Te = 1∶0.5~0.7 is controlled. After the state stabilizes, the molecular beam main baffle is opened, and the epitaxial growth of CdTe thin film 3 begins. By controlling the growth time, films of different thicknesses can be obtained.

[0023] Step 5: Peeling-Transfer Wafer-Level Self-Supporting CdTe Film. Specifically, the CdTe film 3, 2D material 1, and sapphire substrate 2 are removed from the heating support. Thermally released adhesive tape 4 (polydimethylsiloxane) is tightly adhered to the surface of the CdTe film 3. All are then immersed in deionized water for 24 hours. The water molecules disrupt the weak van der Waals interactions between the CdTe film and the substrate, causing the CdTe film to separate from the substrate. The thermally released adhesive tape 4 with the CdTe film adhered is then adhered to the silicon substrate, and heating at 90-100°C for 3-5 minutes breaks the adhesiveness of the thermally released adhesive tape 4, resulting in a self-supporting CdTe film. (See attached image for physical sample). Figure 2 As shown, see the scanning electron microscope image. Figure 3 As shown.

[0024] See Figure 4 The figure shows the high-resolution X-ray diffraction spectra of the wafer-level self-supporting CdTe film prepared in this invention on a sapphire substrate and after being transferred to a silicon substrate by peeling-thermal release. As can be seen from the figure, the CdTe film 3 grown on the two-dimensional material 1 / sapphire substrate 2 by the molecular beam epitaxy system is a single crystal film with the crystal growth direction along the

[111] direction; the diffraction peak positions of CdTe before and after the transfer do not change, and the crystallographic properties after growth are maintained.

[0025] The wafer-level self-supporting CdTe film prepared in this embodiment is a single-crystal film with an epitaxial direction along the

[111] crystal orientation and a continuous film height. Due to the weak van der Waals forces at the two-dimensional material interface, the single-crystal CdTe film is easily peeled off from the native substrate and can be transferred to any other substrate. It is compatible with mainstream silicon-based electronic circuits and is suitable for various flexible electronic device requirements.

[0026] This embodiment is merely an example to clearly illustrate the invention and is not intended to limit the implementation. Those skilled in the art should understand that the scope of the present invention includes, but is not limited to, the above embodiments. Various changes made to the present invention in other forms without departing from the spirit or basic characteristics of the present invention are all included within the protection scope of the present invention.

Claims

1. A method for preparing a wafer-level self-supporting CdTe thin film, characterized in that, Includes the following steps: Select a two-dimensional material / sapphire substrate; Cleaning the surface of two-dimensional materials / sapphire substrates; Two-dimensional material / sapphire substrate and substrate heating support are assembled by molten metal material; CdTe thin films were grown on two-dimensional materials / sapphire substrates using a molecular beam epitaxy system. CdTe thin films / two-dimensional materials are peeled off using heat-release adhesive tape; A self-supporting CdTe film is obtained by removing the heat-release adhesive tape through heating; wherein: The two-dimensional material is one of graphene, molybdenum disulfide, and molybdenum ditelluride; the two-dimensional material has a single-layer structure; a CdTe thin film is grown on the single-layer two-dimensional material; The process of growing CdTe thin films on two-dimensional materials / sapphire substrates using a molecular beam epitaxy system is as follows: a CdTe and Te source with a purity of at least 7N is used as the beam source; the equivalent pressure ratio of the beam current is controlled to be CdTe:Te = 1:0.5~0.7; the heating wire temperature is controlled to be 280~300℃; the growth time is controlled to be 10-90 min; the thickness is 50-500 nm; and the growth status of the CdTe thin film is monitored in real time using a reflection high-energy electron diffractometer. The self-supporting CdTe film is a single crystal film with a size of 0.5cm×0.5cm~1cm×1cm. The out-of-plane crystal orientation of the film grown by the molecular beam epitaxy system is along the [111] direction. The process of peeling off the CdTe film / two-dimensional material with heat-release tape is as follows: the heat-release tape, i.e., polydimethylsiloxane, is tightly adhered to the surface of the CdTe film; the air bubbles between the heat-release tape and the CdTe film are squeezed out with a cotton swab until the heat-release tape and the CdTe film are fully bonded together. The heat-release tape is removed by heating, with a heating temperature of 90~110℃ and a heating time of 3~5 minutes. The metal material is indium or a lead-tin alloy; The resulting self-supporting CdTe film can be transferred onto any substrate material.

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