Method for transferring nanometer silicon film to flexible substrate

Abstract

The invention provides a method for transferring a nanometer silicon film to a flexible substrate, which comprises the following steps of: removing a silicon oxide layer of silicon on an insulator by hydrofluoric acid etching, so that the nanometer silicon film is attached to the silicon substrate, and the silicon on the insulator sequentially comprises the silicon substrate, the silicon oxide layer and the nanometer silicon film from bottom to top; sequentially covering the nanometer silicon film with a polypropylene carbonate layer and a polydimethylsiloxane layer, and bonding the nanometer silicon film with the polypropylene carbonate layer; separating the nano silicon film from the silicon substrate, and removing the polydimethylsiloxane layer, so that the nano silicon film is adhered to the polypropylene carbonate layer; and the nanometer silicon film adhered to the polypropylene carbonate layer is attached to the flexible substrate, and the polypropylene carbonate layer is removed. The invention also provides the nanometer silicon film which is formed on the flexible substrate and is obtained by using the method. According to the method for transferring the nanometer silicon film to the flexible substrate, the success rate of transferring the nanometer silicon film can be increased, and the high-quality nanometer silicon film can be obtained on the flexible substrate.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to a nano-silicon film, and more particularly to a method for transferring the nano-silicon film to a flexible substrate. Background Art

[0002] Silicon is a traditional semiconductor that is widely used in the semiconductor manufacturing field in the form of rigid wafers. It can be deduced from the mechanical properties of the material that when its thickness is reduced to the nanometer level, the silicon film has higher flexibility than bulk silicon, which enables it to withstand mechanical stress in the biological environment. At the same time, nano-silicon film will show good stability in the biological environment. As a silicon-based material, nano-silicon film is non-toxic and harmless, and is not easy to cause rejection or toxic reactions in organisms. It is an ideal biocompatible material. Therefore, nano-silicon film can be used to prepare bioelectronic devices that require good flexibility.

[0003] Nano silicon membranes have many applications in the field of bioelectronics. For example, silicon membranes can be made into electrodes or sensor elements, contacted with tissues or body fluids in the body, and accurate measurements of physiological signals can be achieved by detecting changes in electrical signals generated by the interaction between biomolecules and silicon membranes. Specific biorecognition molecules, such as antibodies and nucleic acid aptamers, can also be modified on the surface of silicon membranes. When target biomolecules bind to recognition molecules, the electrical or optical properties of silicon membranes will change, thereby achieving rapid and sensitive detection of biomolecules. At the same time, nano silicon membranes have good biocompatibility and can be widely used in the field of bioelectronics. Summary of the invention

[0004] In view of this, the present invention provides a method for transferring a nano-silicon film to a flexible substrate, so as to form a nano-silicon film with high quality and good electrical properties on the flexible substrate.

[0005] According to an embodiment of one aspect of the present invention, a method for transferring a nano-silicon film to a flexible substrate is provided, comprising:

[0006] The invention discloses a method for removing the silicon oxide layer of the silicon on insulator by etching with hydrofluoric acid, so that the nano silicon film is bonded to the silicon substrate, wherein the silicon on insulator includes the silicon substrate, the silicon oxide layer and the nano silicon film in order from bottom to top; sequentially covering the nano silicon film with a polypropylene carbonate layer and a polydimethylsiloxane layer, and bonding the nano silicon film to the polypropylene carbonate layer; separating the nano silicon film from the silicon substrate, removing the polydimethylsiloxane layer, and bonding the nano silicon film to the polypropylene carbonate layer; and bonding the nano silicon film bonded to the polypropylene carbonate layer to the flexible substrate, and removing the polypropylene carbonate layer.

[0007] According to another embodiment of the present invention, there is provided a nano-silicon film formed on a flexible substrate obtained by the above method.

[0008] According to the method for transferring the nano-silicon film to the flexible substrate provided by the above embodiment of the present invention, hydrofluoric acid etching is used to remove the silicon oxide layer of the silicon on the insulator, the nano-silicon film of the silicon on the insulator is bonded to the polypropylene carbonate layer, and a polydimethylsiloxane layer is used to provide support for the nano-silicon film and the polypropylene carbonate layer to prevent the nano-silicon film from bending and deforming during the transfer process and causing cracks. The method provided by the present invention can improve the success rate of the nano-silicon film transfer and obtain a high-quality nano-silicon film on a flexible substrate.

[0009] According to the method for transferring the nano-silicon film to the flexible substrate provided by the above embodiment of the present invention, the Si(OH) grown on the surface of the nano-silicon film is removed by using reactive ion etching. 4 , which can improve the electrical properties of nano-silicon films. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0011] Figure 1 A schematic diagram of a process for transferring a nano-silicon film to a flexible substrate provided by an embodiment of the present invention;

[0012] Figure 2A to Figure 2E A schematic diagram of a process for removing a silicon oxide layer on a silicon-on-insulator provided by an embodiment of the present invention;

[0013] Figure 3A to Figure 3D A schematic diagram of a transfer process of transferring a nano-silicon film to a flexible substrate provided by an embodiment of the present invention;

[0014] Figure 4 A schematic diagram of removing a silicon oxide layer on a silicon-on-insulator according to an embodiment of the present invention;

[0015] Figure 5 Figure (a) is the XPS graph of the SOI surface after immersion in HF for 6 hours; Figure 5 Figure (b) is the XPS graph of the SOI surface after immersion in HF for 1 min;

[0016] Figure 6 An optical picture of an electrode formed on a nano-silicon film on a flexible substrate provided by an embodiment of the present invention; and

[0017] Figure 7 A comparison chart of electrical performance test results of the nano-silicon film on the flexible substrate provided by an embodiment of the present invention before and after etching by reactive ion etching.

[0018] Description of reference numerals:

[0019] 1-Silicon substrate;

[0020] 2-silicon oxide layer;

[0021] 3-Nano silicon film;

[0022] 4- Photoresist;

[0023] 5-polypropylene carbonate layer;

[0024] 6-polydimethylsiloxane layer;

[0025] 7- Flexible substrate;

[0026] 8- a first electrode;

[0027] 9- Second electrode. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. However, the present invention can be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, providing these embodiments will make the invention thorough and complete and fully convey the scope of the present invention to those skilled in the art. In the accompanying drawings, for clarity, the sizes and relative sizes of layers and regions may be exaggerated, and the same reference numerals throughout represent the same elements.

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0030] In the related art, single-crystal nano-silicon film cannot be obtained by direct epitaxy, and the polycrystalline nano-silicon film obtained by the deposition method has the problem of poor film quality and high temperature during deposition. In other words, it is difficult to directly deposit single-crystal nano-silicon film on a flexible substrate. The formation of single-crystal nano-silicon film on a flexible substrate by the transfer method in the related art has the problem of easy breakage during the transfer process and poor electrical properties of the transferred single-crystal nano-silicon film.

[0031] In view of this, in order to solve the technical problems in the related art of low transfer success rate of single crystal nano-silicon films and poor quality of the transferred single crystal nano-silicon films, the present invention provides a method for transferring single crystal nano-silicon films to a flexible substrate, so as to improve the transfer success rate of the single crystal nano-silicon films and form high-quality single crystal nano-silicon films on the flexible substrate.

[0032] Figure 1A schematic flow chart of a method for transferring a nano-silicon film to a flexible substrate provided in an embodiment of the present invention.

[0033] Figure 2A to Figure 2E A schematic diagram of a process for removing a silicon oxide layer on a silicon-on-insulator provided in an embodiment of the present invention.

[0034] Figure 3A to Figure 3D A schematic diagram of a transfer process of transferring a nano-silicon film to a flexible substrate provided in an embodiment of the present invention.

[0035] According to an exemplary embodiment of the present invention, the present invention provides a method for transferring a nano-silicon film to a flexible substrate, referring to Figure 1 , Figure 2A to Figure 2E As shown, it includes operations S1 to S4.

[0036] In operation S1, the silicon oxide layer 2 of the silicon on insulator is removed by hydrofluoric acid etching, so that the nano silicon film 3 is attached to the silicon substrate 1, wherein the silicon on insulator includes the silicon substrate 1, the silicon oxide layer 2, and the nano silicon film 3 from bottom to top, and the nano silicon film 3 is a single crystal nano silicon film.

[0037] In some embodiments, the silicon on insulator (SOI) is a commercial SOI (001). Figure 2A As shown, the silicon-on-insulator includes, from bottom to top, a 675 μm thick silicon substrate 1, a 375 nm thick silicon oxide layer 2, and a 200 nm thick nano-silicon film (top silicon) 3.

[0038] According to an embodiment of the present invention, before etching the SOI with hydrofluoric acid (HF), the SOI is cleaned with acetone and isopropyl alcohol (IPA) to remove impurities on the SOI.

[0039] In some embodiments, removing the silicon oxide layer 2 of the silicon-on-insulator by etching with hydrofluoric acid includes: operations S11 to S14.

[0040] In operation S11 , the silicon-on-insulator is immersed in hydrofluoric acid to etch and remove a portion of the silicon oxide layer 2 of the silicon-on-insulator, and to form a groove in the silicon oxide layer 2 .

[0041] In some embodiments, the concentration of hydrofluoric acid is 30% to 50%, for example, 30%, 35%, 40%, 45%, 50%, but not limited to the above values. If the concentration of hydrofluoric acid is too low, the etching rate is too slow, which is not conducive to improving the preparation efficiency.

[0042] In some embodiments, reference Figure 2B As shown, SOI was immersed in 40% HF for 5 min, and the SiO 2 A circle of groove (or notch) is etched in the layer.

[0043] In operation S12 , the photoresist 4 is filled in the groove of the silicon oxide layer 2 .

[0044] In some embodiments, reference Figure 2C As shown, photoresist is spin-coated on the surface and groove of the SOI soaked in HF. The photoresist is positive photoresist s1813. After drying, exposure and development, the photoresist outside the groove is developed and removed. Since the nano-silicon film above the groove provides a natural hard mask, the photoresist in the groove will not be developed and removed, so that the groove of the silicon oxide layer 2 is filled with photoresist 4.

[0045] In operation S13 , the silicon-on-insulator is immersed in hydrofluoric acid again to remove the remaining portion of the silicon oxide layer 2 .

[0046] In some embodiments, the SOI is immersed in 40% HF for 6 hours again to remove the remaining portion of the silicon oxide layer 2, so that the silicon oxide layer 2 is completely removed.

[0047] According to an embodiment of the present invention, referring to Figure 2D As shown, the photoresist 4 is filled in the groove of the silicon oxide layer 2, so that after the silicon oxide layer 2 is completely etched away, the silicon substrate 1 and the nano-silicon film 3 have adhesion, preventing the nano-silicon film 3 from being suspended in the hydrofluoric acid solution or shifting from the original position.

[0048] In operation S14, the photoresist 4 is removed.

[0049] In some embodiments, reference Figure 2E As shown, the SOI with the silicon oxide layer 2 removed is soaked in acetone for 1 minute, and then cleaned with anhydrous ethanol to remove the photoresist 4 under the nano-silicon film 3, so that the nano-silicon film 3 is directly attached to the silicon substrate 1.

[0050] In operation S2 , a polypropylene carbonate layer (PPC) 5 and a polydimethylsiloxane layer (PDMS) 6 are sequentially covered on the nano-silicon film 3 , and the nano-silicon film 3 and the polypropylene carbonate layer 5 are bonded.

[0051] In some embodiments, after removing the silicon oxide layer 2 of the SOI, anhydrous ethanol is dripped on the nano-silicon film 3, and the PPC layer 5 and the PDMS layer 6 are sequentially covered. Figure 3B The function of anhydrous ethanol is to facilitate the flattening of the PPC layer, and the function of the PDMS layer is to provide certain support for the PPC layer.

[0052] According to the embodiment of the present invention, the polypropylene carbonate layer 5 covering the nano-silicon film 3 is subjected to a heat treatment so that the nano-silicon film 3 and the PPC layer 5 are bonded.

[0053] In some embodiments, the temperature of the heating treatment is 40°C to 90°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, but not limited to the values ​​listed above. If the temperature is too high, for example, the temperature exceeds 100°C, the polypropylene carbonate may be too soft or wrinkled, and if the temperature exceeds 200°C, the polypropylene carbonate will sublime; if the temperature is too low, the viscosity provided by the polypropylene carbonate is insufficient; that is, if the temperature is too high or too low, the polypropylene carbonate cannot be well bonded to the nano-silicon film.

[0054] According to an embodiment of the present invention, in the process of transferring the nano silicon film, the nano silicon film is adhered thereto by using a PPC (polypropylene carbonate) film. PPC softens when heated and can provide greater adhesion. In addition, a thicker PDMS (polydimethylsiloxane) material is used to support the PPC on the back to prevent it from deforming. The silicon film may break when the deformation exceeds 1%. By using a PPC layer and a PDMS layer to transfer the nano silicon film, the deformation of the nano silicon film can be avoided, and the nano silicon film can be made less likely to break.

[0055] In operation S3 , the nano-silicon film 3 is separated from the silicon substrate 1 , and the polydimethylsiloxane layer 6 is removed, so that the nano-silicon film 3 adheres to the polypropylene carbonate layer 5 .

[0056] According to an embodiment of the present invention, since there is almost no force between the nano-silicon film 3 and the silicon substrate 1, the adhesion between the PPC layer 5 and the nano-silicon film 3 is stronger than the adhesion between the nano-silicon film 3 and the silicon substrate 1, and the nano-silicon film 3 is peeled off from the silicon substrate 1. At this time, the nano-silicon film 3 will adhere to the PPC layer 5, and then the PDMS layer 6 is peeled off from the PPC layer 5 to remove the PDMS layer 6.

[0057] In operation S4 , the flexible substrate 7 is bonded to the nano-silicon film 3 , and the polypropylene carbonate layer 5 is removed.

[0058] According to the embodiment of the present invention, the material of the flexible substrate 7 is not limited here, and can be, for example, a polyimide film (PI) or an Ecoflex film.

[0059] refer to Figure 3C , Figure 3D As shown, the nano-silicon film 3 adhered to the PPC layer 5 is attached to the flexible substrate 7. The PPC layer 5, the nano-silicon film 3 and the flexible substrate 7 adhered together are immersed in anisole for more than 12 hours to dissolve and remove the PPC layer 5, thus completing the transfer of the nano-silicon film 3 to the flexible substrate 7.

[0060] According to multiple experiments, after SOI is immersed in concentrated HF for a long time and the silicon oxide layer is removed by hydrofluoric acid, the nano-silicon film becomes non-conductive or its electrical properties degrade. This is because the reactions shown in reaction equations (1) and (2) occur during the process of removing the silicon oxide layer on the insulator by HF etching.

[0061] SiO 2 +6HF→H 2 SiF 6 Formula (1)

[0062] H 2 SiF 6 +4H 2 O→Si(OH) 4 +6HF formula (2)

[0063] According to an embodiment of the present invention, referring to Figure 4 As shown, HF and SiO 2 Reaction to generate Si(OH) 4 ,Si(OH) 4 Deposited on the surface of the nano-silicon film, causing the electrical properties of the nano-silicon film to deteriorate. The Si(OH) generated on the nano-silicon film is removed by reactive ion etching. 4 , which can improve the electrical properties of nano-silicon films.

[0064] Figure 5 Figure (a) is the XPS graph of the SOI surface after immersion in HF for 6 hours; Figure 5 Figure (b) is the XPS graph of the SOI surface after soaking in HF for 1 min.

[0065] refer to Figure 5 As shown in Figure (a), the XPS test results show that after SOI is immersed in hydrofluoric acid (HF) for 6 hours, a large number of residual Si-O bonds can be detected on the SOI surface. It is speculated that the Si-O bonds come from Si(OH) 4 . refer to Figure 5 As shown in Figure (b), the XPS test results show that after SOI is immersed in concentrated HF for 1 min, the peak of Si-O bond on the SOI surface is very weak, which indicates that there is no SiO generated by natural oxidation on the SOI surface. 2 , which can explain Figure 5 The Si-O bonds detected on the SOI surface in Figure (a) come from Si(OH) deposited on the surface. 4 .

[0066] According to an embodiment of the present invention, the transferred nano-silicon film is processed by reactive ion etching (RIE) to remove Si(OH) generated on the surface of the nano-silicon film during the process of etching and removing the silicon oxide layer. 4 , to improve the conductive effect of nano-silicon film.

[0067] In some embodiments, etching the transferred nano-silicon film by reactive ion etching includes: introducing a reactive gas into the vacuum chamber, the reactive gas being, for example, SF 6 , CHF 3 , the gas pressure is 20mTorr, the power is 200w, the etching time is 10s, the etching depth is 10~30nm, for example, 10nm, 15nm, 20nm, 30nm, but not limited to the listed values.

[0068] According to an exemplary embodiment of the present invention, the present invention provides a nano-silicon film formed on a flexible substrate obtained by the above method.

[0069] According to an embodiment of the present invention, the present invention provides an application of a nano silicon film formed on a flexible substrate in a transistor and a sensor.

[0070] Figure 6 An optical picture of an electrode formed on a nano-silicon film on a flexible substrate provided by an embodiment of the present invention.

[0071] refer to Figure 6 As shown, a complete nano-silicon film 3 is formed on a flexible substrate 7, a first electrode 8 and a second electrode 9 are respectively formed on the nano-silicon film 3, and the electrical properties of the nano-silicon film are obtained through electrical testing.

[0072] In some embodiments, the first electrode 8 is, for example, Ti / Au, and the second electrode 9 is, for example, Ti / Au, for example, 10 nm Ti and 40 nm Au.

[0073] Figure 7 A comparison chart of electrical performance test results of the nano-silicon film on the flexible substrate provided by an embodiment of the present invention before and after etching by reactive ion etching.

[0074] See also Figure 7 As shown in the figure, after the nano-silicon film is transferred to the flexible substrate, before the nano-silicon film is etched by reactive ion etching, the current of the nano-silicon film is almost 0, which indicates that the electrical performance of the nano-silicon film is poor. After the nano-silicon film is etched by reactive ion etching, the current of the nano-silicon film is significantly improved, which indicates that the electrical performance of the nano-silicon film etched by reactive ion etching is significantly improved compared with the nano-silicon film not etched by reactive ion etching.

[0075] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for transferring a nano-silicon film to a flexible substrate, characterized in that: include: The silicon oxide layer (2) of the silicon-on-insulator is removed by hydrofluoric acid etching, so that the nano silicon film (3) is attached to the silicon substrate (1), wherein the silicon-on-insulator comprises, from bottom to top, the silicon substrate (1), the silicon oxide layer (2), and the nano silicon film (3); sequentially covering the nano silicon film (3) with a polypropylene carbonate layer (5) and a polydimethylsiloxane layer (6), and bonding the nano silicon film (3) to the polypropylene carbonate layer (5); Separating the nano-silicon film (3) from the silicon substrate (1), and removing the polydimethylsiloxane layer (6), so that the nano-silicon film (3) adheres to the polypropylene carbonate layer (5); and The nano silicon film (3) adhered to the polypropylene carbonate layer (5) is bonded to a flexible substrate (7), and the polypropylene carbonate layer (5) is removed.

2. The method according to claim 1, characterized in that: Removing the silicon oxide layer (2) of silicon on an insulator by etching with hydrofluoric acid comprises: Soaking the silicon-on-insulator in hydrofluoric acid to etch and remove a portion of the silicon oxide layer (2) of the silicon-on-insulator, thereby forming a groove on the silicon oxide layer (2); Filling the groove of the silicon oxide layer (2) with photoresist (4); soaking the silicon-on-insulator in hydrofluoric acid again to remove the remaining portion of the silicon oxide layer (2); and The photoresist (4) is removed.

3. The method according to claim 2, characterized in that The concentration of hydrofluoric acid is 30%~50%.

4. The method according to claim 2, characterized in that: The photoresist is a positive photoresist.

5. The method according to claim 1, characterized in that Bonding the nano silicon film (3) to the polypropylene carbonate layer (5) comprises: Heat-treating the polypropylene carbonate layer (5) covering the nano-silicon film (3) so that the nano-silicon film (3) and the polypropylene carbonate layer (5) are bonded together; The heating temperature is 40°C to 90°C.

6. The method according to claim 1, characterized in that Removing the polypropylene carbonate layer (5) comprises: The polypropylene carbonate layer (5) is dissolved and removed by using anisole.

7. The method according to claim 1, characterized in that Also includes: The nano-silicon film transferred onto the flexible substrate is etched by reactive ion etching to remove Si(OH)4 generated on the surface of the nano-silicon film in the process of etching and removing the silicon oxide layer.

8. The method according to claim 7, characterized in that The etching depth of the reactive ion etching method is 10-30 nm.

9. A nano-silicon film formed on a flexible substrate obtained by the method according to any one of claims 1 to 8.

10. Application of the nano-silicon film formed on a flexible substrate as claimed in claim 9 in transistors and sensors.

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