A transfer device and a transfer method for low-dimensional thin films

Abstract

This invention discloses a transfer device and method for low-dimensional thin films, belonging to the field of materials science and technology. The transfer device includes a tank containing a base, with a support frame mounted above the base. A spinning assembly is mounted on the support frame. The spinning assembly includes a spinning column and an eccentric floating joint and a pressure head sequentially connected below the spinning column. The spinning column and the support frame are movably connected via a connecting mechanism. During the low-dimensional thin film transfer process, rotating the spinning column causes the pressure head to move downwards, pressing the sample to be transferred tightly against the target substrate. Adding liquid to the tank removes the sacrificial layer, separating the thin film from the original substrate. Subsequent heat treatment achieves the transfer of the functional thin film to the target substrate. This device and method can compensate for flatness deviations between the sample and the substrate, reduce local stress concentration, improve the integrity of low-dimensional thin film transfer, and the transfer process does not require a flexible support substrate.

Description

Technical Field

[0001] This invention belongs to the field of materials science and technology, and more specifically, relates to a transfer device and method for low-dimensional thin films. Background Technology

[0002] With the continuous development of micro- and nano-electronic devices, information storage devices, and novel functional electronic devices, heterogeneous integration and transfer technologies for low-dimensional thin films such as ultrathin ferroelectric thin films have attracted widespread attention. Especially in ferroelectric tunnel junction devices, the ferroelectric thin film layer typically serves as a tunneling barrier layer, with a thickness usually on the nanoscale. To achieve the integration of low-dimensional thin films such as ferroelectric thin films with current silicon semiconductor processes, a sacrificial layer, such as the water-soluble sacrificial layer Sr4Al2O7 (SAO), is usually placed between the original substrate and the low-dimensional thin film. Due to the thinness of both the sacrificial layer and the low-dimensional thin film, the entire thin film system has low mechanical strength during release, bonding, and transfer, making it susceptible to uneven internal and external stresses, leading to problems such as cracking and wrinkling.

[0003] In existing technologies, low-dimensional thin film transfer typically employs a polymer support layer or a flexible substrate to support the transferred low-dimensional thin film. After the sacrificial layer is dissolved in water, the low-dimensional thin film is then transferred to the target substrate. While these methods can achieve low-dimensional thin film transfer to a certain extent, they still have the following shortcomings for the ultrathin SAO / ferroelectric layer system involved in ferroelectric tunnel junctions: Firstly, the introduction of a polymer support layer or flexible substrate can easily lead to organic residues, which is detrimental to obtaining a clean transfer interface. Secondly, ultrathin thin films themselves have weak resistance to deformation; if the force is uneven or there is localized stress concentration during the transfer process, cracks, damage, or defects can easily occur. Furthermore, it is usually difficult to maintain a good planar fit between the sample to be transferred and the target substrate. When there is a planarity deviation between the two, it can easily affect the uniformity of the fit and the final transfer quality.

[0004] Therefore, it is necessary to provide a transfer device and method suitable for ultrathin self-supporting functional films, especially for ultrathin SAO sacrificial layers and ultrathin ferroelectric layer systems in ferroelectric tunnel junctions, so as to achieve stable adhesion, uniform pressure and reliable release in a liquid environment of the low-dimensional film to be transferred to the target substrate without the aid of a flexible support substrate, thereby improving the integrity, stability and consistency of low-dimensional film transfer. Summary of the Invention

[0005] To address the problems in existing technologies where low-dimensional thin films suffer from cracking and wrinkling during transfer due to low mechanical strength and uneven stress, or where organic residues are easily introduced when using polymer support layers or flexible substrates for transfer, this invention provides a transfer device and method for low-dimensional thin films. This method achieves stable adhesion, uniform pressure, and stable release in a liquid environment between the low-dimensional thin film to be transferred and the target substrate without the aid of a flexible substrate, thereby improving the integrity of low-dimensional thin film transfer.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention is to provide a transfer device for low-dimensional thin films, comprising: a tank, a base placed inside the tank, a support frame mounted above the base, and a spinning assembly mounted on the support frame; The spinning assembly includes a spinning column, an eccentric floating joint, and a pressure head. The eccentric floating joint connects the spinning column and the pressure head. The eccentric floating joint allows the pressure head to adaptively deflect relative to the spinning column to compensate for flatness deviations between the sample to be transferred and the target substrate. The bottom surface of the pressure head is horizontal. The spinning column and the support frame are movably connected via a connecting mechanism, allowing the spinning column to move vertically relative to the support frame. By rotating the spinning column, the pressure head moves downwards vertically and transmits pressure to the sample to be transferred via the eccentric floating joint, thereby pressing the sample to be transferred tightly against the target substrate. The eccentric floating joint allows the pressure head to adaptively deflect relative to the spinning column to compensate for flatness deviations between the sample to be transferred and the target substrate, reducing local stress concentration and improving bonding uniformity.

[0007] As a preferred technical solution, a clamping assembly is further included for clamping the target substrate. The clamping assembly includes a fixed clamping part and a movable clamping part. Both the fixed clamping part and the movable clamping part are mounted above the base and arranged opposite to each other, with the target substrate located between the fixed clamping part and the movable clamping part. The movable clamping part includes a limiting plate, a movable plate, and an elastic component connecting the limiting plate and the movable plate. The limiting plate is fixedly connected to the top of the base. The movable plate moves towards the fixed clamping part under the action of the elastic component to clamp the target substrate. Through the cooperation of the fixed clamping part and the movable clamping part, target substrates of different sizes and specifications can be clamped. More preferably, the elastic component includes a spring and a sleeve, with the spring housed inside the sleeve to reduce the corrosive effect of liquid on the spring. Specifically, the sleeve includes two sets of parallel hollow cylindrical sleeves, with the spring disposed inside the two hollow cylindrical sleeves.

[0008] As a preferred technical solution, the connecting mechanism is a threaded connection mechanism; it includes a threaded hole provided on the support frame and an external thread provided outside the spinning column and threadedly connected to the threaded hole.

[0009] As a preferred technical solution, the support frame is a portal frame, including two support columns symmetrically fixed above the base and a crossbeam fixed to the top of the support columns; the threaded hole is located in the middle of the crossbeam.

[0010] As a preferred technical solution, the tank is used to contain the liquid, and the lateral dimension of the tank is larger than the lateral dimension of the base. Preferably, the liquid level in the tank is higher than the interface between the sample to be transferred and the target substrate, so as to ensure that the liquid can fully act on the structure to be released.

[0011] A second aspect of the present invention is to provide a method for transferring low-dimensional thin films, which is performed using the transfer apparatus described in the first aspect above, and includes the following steps: The target substrate is placed on the base; preferably, the target substrate is a semiconductor substrate such as a silicon substrate. The sample to be transferred is placed above the target substrate, with the low-dimensional film in the sample facing the target substrate. The sample to be transferred, from bottom to top, includes the original substrate, the sacrificial layer, and the low-dimensional film to be transferred. Preferably, the low-dimensional film is a transition metal oxide film such as a ferroelectric film. The original substrate is a single-crystal oxide substrate. The sacrificial layer is a water-soluble layer or an intermediate layer that can be removed in a liquid. Since the sacrificial layer can be dissolved, peeled off, or structurally destroyed under the action of liquid, the low-dimensional film to be transferred can be separated from the original substrate. Rotate the spinning column to move the pressure head downwards through the eccentric floating joint, so that the sample to be transferred is pressed tightly against the target substrate; A liquid capable of dissolving the sacrificial layer is added to the tank and the immersion is maintained for 20–28 hours to dissolve the sacrificial layer, thereby separating the low-dimensional film to be transferred from the original substrate; preferably, the liquid is water. After soaking, the target substrate of the laminated low-dimensional film is heated to a temperature of 95–115 °C to vaporize the residual liquid and promote further opening of the incompletely separated areas, thereby realizing the transfer of the low-dimensional film to be transferred to the target substrate.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention enables the transfer of ultrathin functional films without the aid of a polymer support layer or a flexible support substrate. In the prior art, polymer support layers or flexible support substrates are often used to assist in supporting the film to be transferred, but these auxiliary materials often have the problem of easily generating organic residues after transfer. Especially for device structures such as ferroelectric tunnel junctions, which have high requirements for interface cleanliness, interface contamination can easily affect the performance and stability of the device. This invention completes the transfer by combining mechanical pressing and liquid dissolution, without the need for a flexible support substrate, which is conducive to obtaining a clean and stable interface.

[0013] (2) This invention enables continuous adhesion between the sample to be transferred and the target substrate during the transfer process, which is beneficial to improving the integrity of the transfer. By setting up a gate-shaped support and a spinning assembly, this invention can maintain the sample to be transferred and the target substrate in a stable and compacted state during the removal of the sacrificial layer, so that the functional film to be transferred is always supported and received by the target substrate during the release process. Compared with the method of releasing first and then transferring or the unstable adhesion during the release process, this invention can effectively reduce the situation of the film floating, suspending, shifting or partially collapsing in the liquid, thereby improving the integrity and continuity of film transfer.

[0014] (3) The present invention, through the setting of the eccentric floating joint, can compensate for the flatness deviation between the sample to be transferred and the target substrate, and improve the uniformity of interface bonding. In actual operation, it is usually difficult to achieve an ideal absolute parallel state between the sample to be transferred, the target substrate, and the pressure head. If the pressure head is directly rigidly pressed, it is easy to cause local contact first and excessive local stress, which can lead to film cracking, wrinkling, or poor local bonding. The eccentric floating joint in the present invention allows the pressure head to undergo a certain degree of adaptive sway during the pressing process, thereby automatically compensating for the small planar error between the sample and the substrate, making the pressure distribution more uniform and reducing local stress concentration.

[0015] (4) This invention helps reduce the risk of mechanical damage to the sacrificial layer and low-dimensional film during the transfer process. Due to the small overall thickness of the sacrificial layer and low-dimensional film, the film system has low mechanical strength and is extremely sensitive to stress. This invention provides controllable downward pressure through spinning columns, achieves flexible compensation through eccentric floating joints, and maintains stable positioning of the target substrate through clamping components. Structurally, this reduces stress concentration caused by misalignment, tilting, and local overload during the pressing process, which helps reduce problems such as cracks, breakage, wrinkles, warping, and interface damage.

[0016] (5) The present invention can further promote the removal of residual liquid and the opening of incompletely separated areas through heat treatment, which is beneficial to improving the final transfer effect. After the soaking and release is completed, the bonded sample is heated to vaporize the residual liquid and promote the further opening of the local incompletely separated areas, which is beneficial to the complete separation of the functional film to be transferred from the original substrate and enhances the adhesion between the functional film and the target substrate, thereby further improving the transfer success rate and transfer quality.

[0017] (6) The clamping assembly in this invention can adapt to target substrates of different sizes and has good versatility. By setting a fixed clamping part and a movable clamping part, and making the movable clamping part move towards the fixed clamping part under the action of the elastic component, this invention can stably clamp target substrates of different sizes. Compared with clamping structures with fixed size and poor adaptability, the device of this invention has a wider range of applications and can meet the experimental and preparation needs of different substrate specifications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the transfer device provided by the present invention; Figure 2 for Figure 1 Schematic diagram of the structure after removing the tank body; Figure 3 for Figure 2 The front view; Figure 4 This is a schematic diagram of the layered structure of the sample to be transferred. Figure 5 These are optical microscope comparison images of samples obtained in the examples and comparative examples; Reference numerals: 1-base; 2-fixed clamping part; 3-support column; 4-eccentric floating joint; 5-crossbeam; 6-spinning column; 7-movable clamping part; 71-limiting plate; 72-movable plate; 73-elastic component; 74-clamping block; 8-target substrate; 9-sample to be transferred; 10-pressure head; 11-groove; 12-STO substrate; 13-SAO sacrificial layer; 14-low-dimensional thin film. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art. All eccentric floating joints, pressure heads, etc. in the present invention are standard parts and can be purchased commercially.

[0020] It should be noted that in this invention, terms such as "fixed connection," "installation," and "connection" all indicate that two interconnected components are fixed together, typically by welding or screws. "Movable installation" refers to two components connected together that can move relative to each other.

[0021] In the description of this invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations of this invention.

[0022] It should be noted that the "low-dimensional thin film" mentioned in this invention refers to an ultra-thin functional thin film with a thickness at the nanoscale, low mechanical strength in a self-supporting state, and easy to break and wrinkle, such as ferroelectric thin films, piezoelectric thin films, or magnetic thin films, and is especially suitable for ultra-thin low-dimensional thin films of transition metal oxides such as ferroelectric layers in ferroelectric tunnel junctions.

[0023] Example 1 like Figures 1 to 3 As shown, the transfer device provided in this embodiment includes a tank 11, a base 1 disposed within the tank 11, a portal frame disposed above the base 1, and a spinning assembly disposed on the portal frame. The portal frame consists of two opposing support columns 3 and a crossbeam 5 connected to the top of the two support columns 3. The crossbeam 5 is provided with threaded mounting holes, and the spinning column 6 is threadedly engaged with the threaded mounting holes. The lower end of the spinning column 6 is sequentially connected to an eccentric floating joint 4 and a pressure head 10.

[0024] A clamping assembly for fixing a target substrate 8 is provided on the base 1. The clamping assembly includes a fixed clamping part 2 and a movable clamping part 7. The movable clamping part 7 can be connected to an elastic component so that it can move toward the fixed clamping part 2 during use, thereby clamping and positioning target substrates 8 of different sizes. The specific structure of the movable clamping part 7 is shown in the reference [reference needed]. Figure 2 The system includes a limiting plate 71, a movable plate 72, and an elastic component 73 connecting the limiting plate 71 and the movable plate 72. The limiting plate 71 is fixedly connected to the top of the base. The movable plate 72 moves towards the fixed clamping part under the action of the elastic component and clamps the target substrate. Specifically, a snap-fit ​​block 74 is fixed to the top of the limiting plate 71 at the end away from the fixed clamping part. The target substrate is limited between the snap-fit ​​block and the movable clamping part 73. The elastic component is not shown separately in the figure, but it can be a structure of spring and sleeve.

[0025] like Figure 4 As shown, the sample 9 to be transferred in this embodiment has a layered structure, comprising, from bottom to top, an STO substrate 12, a SAO sacrificial layer 13, and a low-dimensional thin film 14. The STO substrate 12 serves as the original substrate, the SAO sacrificial layer 13 is a sacrificial layer that can be removed in water, and the low-dimensional thin film 14 is the thin film to be transferred. The target substrate 8 can be a rigid substrate.

[0026] Example 2 This embodiment uses a silicon substrate as the target substrate and the ferroelectric layer in the ferroelectric tunnel junction as a low-dimensional thin film as an example. The method for transferring the low-dimensional thin film using the transfer device in Example 1 includes the following steps: First, the target substrate 8 is placed on the base 1, and the target substrate 8 is clamped and limited by the fixed clamping part 2 and the movable clamping part 7 to keep it stable during the subsequent pressing and immersion process. Then, the sample 9 to be transferred is placed above the target substrate 8, with the low-dimensional film 14 facing the target substrate 8.

[0027] Next, the spinning column 6 is rotated, causing the pressure head 10 to move vertically downwards under the drive of the eccentric floating joint 4 until the sample 9 to be transferred is pressed tightly against the target substrate 8. During this process, the eccentric floating joint 4 can compensate for the flatness deviation between the sample 9 to be transferred and the target substrate 8 to a certain extent, thereby reducing the problem of excessive local force, making the pressing process more stable and the pressure distribution more uniform.

[0028] After the sample is compressed, liquid is added to the tank 11 so that the liquid level is higher than the bonding interface between the sample 9 to be transferred and the target substrate 8. In this embodiment, deionized water is used as the liquid. The sample is immersed at room temperature for 24 hours. During this process, the SAO sacrificial layer 13 gradually dissolves, and the low-dimensional film 14 separates from the STO substrate 12 while maintaining its adhesion to the target substrate 8, thereby completing the release process.

[0029] After soaking, the bonded sample is removed and heated at 100 °C for 10 min to remove residual moisture at the interface and promote further opening of the incompletely separated local areas, thereby improving the integrity of the transfer of the low-dimensional film 14 to the target substrate 8.

[0030] After the transfer was completed, the sample surface was observed using an optical microscope at a magnification of 100x. The results are as follows. Figure 5 As shown in Figure b, the sample surface after transfer using the device of the present invention is generally smooth and continuous, with no obvious large-area wrinkles or severe cracks, and only a few sporadic damages. This indicates that the device of the present invention can effectively achieve stable release and transfer of the ultrathin SAO sacrificial layer / ultrathin low-dimensional film system.

[0031] Comparative Example 1 To illustrate the advantages of the present invention, a comparison was made using a PDMS-assisted transfer method under the same conditions of the sample to be transferred and the same target substrate.

[0032] The sample to be transferred was the same as in Example 1, consisting of a layered structure of STO substrate 12 / SAO sacrificial layer 13 / low-dimensional thin film 14, and the target substrate 8 also used a silicon substrate of the same specifications. The specific process is as follows: First, a PDMS auxiliary layer was attached to the side of the low-dimensional thin film 14 away from the SAO sacrificial layer 13, so that the PDMS auxiliary layer would act as a flexible carrier during the subsequent release process; then, the entire sample was immersed in deionized water to gradually dissolve the SAO sacrificial layer 13, thereby separating the low-dimensional thin film 14 from the STO substrate 12 under the support of the PDMS auxiliary layer; then, the low-dimensional thin film 14 supported by the PDMS auxiliary layer was transferred to the surface of the target substrate 8 and bonded together.

[0033] After the transfer in Comparative Example 1 was completed, the sample surface was observed using a 100x optical microscope, and the results are as follows. Figure 5 As shown in Figure a, the sample surface obtained using the PDMS-assisted transfer method exhibits noticeable wrinkles and poor surface uniformity. Figure 5 Compared to the results shown in Figure b, the sample surface obtained using the self-supporting thin film transfer device of the present invention is smoother and wrinkles are significantly reduced, indicating that the method of the present invention is more conducive to maintaining the integrity of ultrathin ferroelectric thin films and helps to improve the stability and consistency of the transfer interface.

[0034] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A transfer device for low-dimensional thin films, characterized in that, Includes: a tank, a base placed inside the tank, a support frame mounted above the base, and a spinning assembly mounted on the support frame; The spinning assembly includes a spinning column, an eccentric floating joint, and a pressure head. The eccentric floating joint is connected between the spinning column and the pressure head, and allows the pressure head to adaptively yaw relative to the spinning column. The spinning column is movably connected to the support frame via a connecting mechanism, and the spinning column can move vertically relative to the support frame under the action of the connecting mechanism. The bottom surface of the pressure head is horizontal.

2. The low-dimensional thin film transfer device according to claim 1, characterized in that, It also includes a clamping assembly; the clamping assembly includes a fixed clamping part and a movable clamping part; the fixed clamping part and the movable clamping part are both installed above the base and arranged opposite to each other; the movable clamping part includes a limiting plate, a movable plate and an elastic component connecting the limiting plate and the movable plate, the limiting plate being fixedly connected to the top of the base; The movable plate moves toward the fixed clamping part under the action of the elastic component.

3. The low-dimensional thin film transfer device according to claim 2, characterized in that, The elastic component includes a spring and a sleeve, with the spring housed inside the sleeve.

4. The low-dimensional thin film transfer apparatus according to any one of claims 1 to 3, characterized in that, The connecting mechanism is a threaded connection mechanism; it includes a threaded hole provided on the support frame and an external thread provided outside the spinning column and threadedly connected to the threaded hole.

5. The low-dimensional thin film transfer device according to claim 4, characterized in that, The support frame is a portal frame, including two support columns symmetrically fixed above the base and a crossbeam fixed to the top of the support columns; The threaded hole is located in the middle of the crossbeam.

6. A method for transferring low-dimensional thin films, characterized in that, It is accomplished using the transfer device as described in any one of claims 1 to 5, and includes the following steps: Place the target substrate on the base; The sample to be transferred is placed above the target substrate, with the low-dimensional film in the sample facing the target substrate; the sample to be transferred, from bottom to top, includes the original substrate, the sacrificial layer, and the low-dimensional film to be transferred. Rotate the spinning column to move the pressure head downwards via the eccentric floating joint, so that the sample to be transferred is pressed tightly against the target substrate; A liquid capable of dissolving the sacrificial layer is added to the tank and kept immersed, so that the sacrificial layer dissolves and the low-dimensional film to be transferred is separated from the original substrate. After soaking, the target substrate of the bonded low-dimensional film is heated to remove residual liquid, thus realizing the transfer of the low-dimensional film to be transferred to the target substrate.

7. The method for transferring low-dimensional thin films according to claim 6, characterized in that, The liquid is water.

8. The method for transferring low-dimensional thin films according to claim 6, characterized in that, The target substrate is a semiconductor substrate; the low-dimensional thin film to be transferred is a transition metal oxide thin film.

9. The method for transferring low-dimensional thin films according to claim 6, characterized in that, The original substrate is a single-crystal oxide substrate; the sacrificial layer is a water-soluble layer or an intermediate layer that can be removed in a liquid.

10. The method for transferring low-dimensional thin films according to claim 6, characterized in that, The soaking time is 20–28 h; the heating temperature is 95–115 ℃.

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